2011 290k miles, Check Hybrid Status last week. Fix or sell?

Short version:

I had a Check Hybrid Status and check engine and various codes last week in my 2011 with 290k miles. Those all went away by themselves, but they scared me enough. I know a lot of pricey repairs are, or might be, upcoming: HV battery replacement, head gasket, brake actuator, water pump, inverter (covered by warranty). But I love this dang car, part of me still wants to make it to 1 million. Do I replace HV battery and drive until inevitably (?) things get worse; or sell now for maybe $3.5k and get some decent used car?

Long version:

Two years ago I got as my first car my parents’ 2011 now with 290k miles, dad did 5k oil changes religiously, EGR cleaned at 260k after maybe 8 months of mild-moderate cold shakes, original HV battery, 12V replaced with third party 6-7 yrs ago, original water pump and inverter.

I suspect an overheating incident occurred one humid afternoon last week: when I went to the car after lunch, auto doors didn’t respond, variety of warning lights (brake ABS steering etc) plus Check Hybrid System, sometimes check engine light. Threw a bunch of sort-of uncommon codes for electronic communication including U0293 P2532 P3107 U0100 U0129 U0151 C1242 etc.

However,

• ⁠I let the car sit totally off for 5 hours as evening and cool air came. By then the only messages were CHS and check engine light, then just CHS, then just CEL.
• This all happened on <2 ticks of gas, the next morning I had only CHS, I filled tank to half, and CHS went away. Since then no lights or messages have reappeared.
  
• After gas I took it to my local hybrid shop. From my description they weren’t totally sure about overheating, but they did say old HV/12V can do weird stuff, and they did confirm low gas does weird stuff with the car’s electric system. They cleared codes, did a short drive and didn’t see ANY codes return.
  
• I’ve taken it on gradually longer drives, yesterday three 1-hour drives with both highway and local, and monitored with Dr Prius. The one and only code that’s reappeared was U0129, which lasted through un- and re-plugging the 12V as well. But…
  
• I cleaned the hybrid fan for the car’s first time last week (I know I know) and battery temps went down from 110F after 10 minutes to maybe 80-90F after 10 minutes. Moreover, U0129 has disappeared. According to Dr Prius I now have no codes at all, battery or engine.
  
• I have not noticed drops in performance or strange sounds/behavior in gas engine, electric motor or regen braking. Braking has arguably felt… meh? for years now, it responds quickly but doesn’t slow the car that quickly if that makes sense. I drove a 2025 rental (non-hybrid) car recently and the brakes felt much more punchy. But I can hear the actuator sounding normally and at normal times, and also I definitely need a brake fluid flush, the fluid is very dark brown / almost black.

Repairs wise:

• The one good Toyota dealer within 60mi of me can’t do work without a CEL or system message etc. They offered to take a look at historical codes from my system in a few weeks. I am eligible for the inverter extended warranty, and my symptoms check out, but I didn’t get any of those key codes that would qualify me for sure. The warranty covers inverter replacement even without codes if I’ve suffered the symptoms, but I have no proof (didn’t take a video of the incident, and symptoms haven’t returned).
• My dad booked a DTC appointment with this car’s dealer, but that’s a few weeks and 600 miles away. Also concerned what they can do without any current DTCs.
• My hybrid shop (that is, the one shop in my small town that even works on / has training on hybrid engines) thinks the HV might be giving up the ghost. Wants to do full inspection before recommending anything like replacement. OEM HV battery plus labor would be $4000, inverter plus labor $1-2000. They charge $175/h diagnosis, which they estimate can take 2-3hr and is separate from the labor they’d charge for any solution. I do trust them (they have a Prius Three as shop car!) but it’s still a high price.

My questions:

• Is the hybrid shop diagnosis worth it? I have no clue what is even damaged at this point if anything. Is my HV too old? Was it the old 12V freaking out in the heat? I also don’t know if anything up front (water pump, inverter, head gasket) is damaged. I think the shop can get clear answers but a possibly $500 inspection seems like a lot. So what are the odds I did have something mechanical damaged from the suspected overheating incident? Should I just wait for the dealer inspection in a few weeks?
• I’d love to keep this car going. My parents feel like it’s not worth the hassle - the EGR cleaning last summer already gave my mom doubts, but I’m willing to do that level of work DIY to keep the car going like my dad did. (He’s on the fence.) I am down to go refurbished for the battery to save $2k, or scrounge dealerships for a discounted OEM and install myself, and find a deal for OEM 12V. If I do these replacements, and continue regular maintenance: How long should I vaguely expect the car to go before other major issues like head gasket, brake actuator, water pump, inverter, etc?
• Say I plug $4k into this car (coming up on new tires soon) and get 2-3 fine years out of it before more stuff breaks. Would that be preferable to trading in for ballpark $3.5k, then buying say a 2019 Prius with 100k for $15k? That would eventually have major maintenance too, but way down the line. Feels like it’s way more upfront cost for more peace of mind plus useless infotainment, unless there’s something I’m missing? Or a 2019 Yaris with 100k for like $10k. Am I just freaking out about buying my “first” car?

Thanks in advance for any advice.

 

Between 20 and 25K a year.