That is the problem with the rebate program the way it is written. While Tesla and GM are about to run out of the incentive, other manufacturers have barely put a dent in theirs. With all these manufacturers just getting into the game, they will have a $7500 advantage over Tesla and GM for years until they get to 200k or the incentive is stopped.
Actually I don't think it will hurt Tesla that badly. These sorts of programs are set up to give an artificial price advantage to emerging technologies to allow them to get established and reach a price point that is closer to on par with the existing tech. The key problem everyone recognized when the program was established was batteries were a lot more expensive than ICE drive trains and so the incentive was to artificially tilt the playing field a bit towards EVs until manufacturers could reduce the cost of batteries to a point where an EV could compete close to an ICE in price.
Tesla did that. They used the time and price advantage the incentive gave them to build the GigaFactory and bring cell prices down to the lowest point ever seen. Now they are sitting on EV gold, they have a factory poised to produce batteries at a much lower price than their competition will be capable of for at least a few years. By the time the rest of the industry is to GF cell prices, Tesla will be making them even cheaper.
When the incentive goes away for Tesla, they could probably do something to effectively reduce the price of their cars (maybe by making current optional features standard, or an actual price cut) which would still leave them with a decent profit per car (though maybe a little reduced), but they probably won't have any serious problems selling their cars without incentive. Without incentive the cost of ownership of the Model 3 is lower than comparable ICE.
GM on the other hand is going to be hurting. They negotiated a sweet deal with LG on batteries for the Bolt, but that's still a limited quantity. They can't produce more than about 50K Bolts a year. LG is taking a loss on Bolt batteries, but they are doing it to learn how to make cars. I expect LG to be a competitor in a few years.
GM will have a hard time moving PHEVs and EVs without the incentive because they didn't figure out how to sell them without the incentive.
I expect GM and other car makers close to losing their incentive to go to Congress asking for some kind of extension. Either that or something from the feds that stops CARB states from mandating the sale of EVs. Though it's likely at least one house of Congress will be in Democrats hands next year and Nancy Pelosi's district has Tesla workers living in it. Congress forcing CARB states to quit requiring EV sales is probably dead in the water, though a new incentive might happen.
If the incentive is allowed to expire, Tesla will do fine. They have been planning to work in an incentive free environment all along and Elon has said he would prefer it (he thinks carbon should be taxed instead). Other car companies will struggle without the incentive though because they haven't figured out how to make compelling cars consumers would want without the incentive.
Is there a final time limit on the entire program?
Congress tried to kill the whole thing as part of the tax bill, but that gambit failed when the auto industry squawked.