If as you say Trump is only waiting for the coast to be clear before firing them, then it's in their interest to make sure the coast is never clear, it would appear to me.
The only way they let Trump walk, I think, is if they reach some agreement that he lets the FBI etc walk too. But I don't think either side trusts each other enough to reach some sort of agreement like that, and the sociopaths on the left aren't known for surrender. Guess we'll see.
It is 100% true that Mueller will drag it out as long as possible, with Sessions’ blessing. However, Trump is a PR genius. He keeps chipping away at Mueller’s investigation. Mueller’s approval #s were much higher at the beginning than they are now. And Trump is anything but finished on that score.
Trump has another huge plus going for him. Having finally gotten the tax cuts, he’s sitting atop an economy that is seething to take off. The better the economy gets, the higher Trump’s approval will rise. The more popular Trump becomes, the more leverage he has.
Things are going Trump’s way. Thanks to Sessions, there are massive speed bumps in the road. But Trump is patient. He’ll strike at just the right time.