Well, yes, of course this is assuming he is stopped from going full dictator. That could easily happen, but it would be terrible for the economy so...and I never thought I'd say this...but thankfully deep pocketed lobbyists will mostly be trying to keep the current state of democracy intact. If we go full monarchy, it's not great for business...
But again, coin flip, end times, and we're all super fucked anyway so the ACA is the least of our concerns.
Providing he doesn't become a dictator, which is certainly probable, his impacts on the environment will be bad, but not catastrophic.
Historically, when the incumbent is out, the president flips to the other party. Businesses plan strategy out for 5-10-20 years. Trump dismantling regulation won't force them to reconsider their strategy entirely. They'll use the 4 years as breathing room knowing it's probable a democratic executive will return in 2029. They'll slow walk progress, but they aren't going to abandon everything and start ramping up emissions. They still have to sell products in CA and the 16 states that follow CA emissions rules. We already saw that in 2016, auto makers stayed the course. They enjoyed the extra time to get their fleet MPGs up, but they knew time would eventually out and they'd need to be competitive when that happened.
Trumps "drill baby drill" plan sounds good to idiots, but oil is still subject to supply and demand. They already lease more land than they could ever use. They'll use trump to buy up leases that would otherwise go to renewables, but they aren't going to start pumping oil past demand and driving their profits down. Especially considering retaliation tariffs could cut into exports as well.
The IRA benefits red states more than blue and they are already begging GOP leaders to leave it alone. Trump might be able to cut individual tax credits for the middle class. Slow some solar and EV purchases, buy that'll cut into Elon's business as well, so maybe he won't even get that done.
Of course, if he goes full dictator, we're fucked anyway. But if he stays within the confines of our flawed democracy, and money prefers he do so they can continue to buy laws forever, then there's a chance his damage will be confined as well.