2013 Charger needs to be replaced, what are your thoughts (also MM question)?

Howdy folks. My fam's 2013 has about 155K miles on it, and unlike a lot of Volts I think it has done at least 100K of them on gas. It stopped charging a couple months ago, Chevy dealer says the charger (silver box near the right front wheel) is bad. On the bright side, it is also expensive ($1500ish) and backordered with no ETA. To the best of my knowledge, the car was still getting 35+ miles per charge but my kids drive the car in another state so I don't see it much any more.

Here are my questions... Do I have any realistic option for replacing the charger other than a dealer? I called a couple places that work on hybrids and EVs and both said if they replaced the part they wouldn't be able to do the programming and at least one gets their parts from the dealership.

Second question, with concerns about the probable life of the propulsion battery AND factoring in a $2500 bill for the charger, what are your thoughts? The car was babied by the original owners, other than apparently doing lots of road trip driving, but my kids have been kinda tough on it. It really needs a new front bumper cover, for instance.

Since the car can't be plugged in to charge, it seems like using MM at least for freeway/highway driving might be a good idea. My understanding is that MM charges the battery to a certain level then stops, so would it make sense to just leave it in MM when not on surface streets?

Thanks, Doug