It isn't going to run out of gas. Without supervision and with unlimited funds from the deep state, Mueller can go on as long as the President is in office. Mueller can spend as much as necessary to harass and ruin everyone around Trump. He has made it clear that the price of being a prominent Trump appointee will be having your life and the lives of your family turned upside down. Congress will not cut off the money. Many of them are avid supporters of the soft coup. So unless Trump fires as many as necessary, they will slowly bleed the Administration to death and stop Trump's agenda. If Trump fires the coup plotters, he might be impeached, but Muller will not stop, otherwise. There will be more high profile indictments and plea bargains. The next one is likely General Flynn who will have been coerced to give damaging statements in exchange for a shorter prison term.
I don't see that. Flynn is the one out of the whole bunch who deserves a pardon (and a medal). Essentually Mueller is done. There is no legal path to charge anyone else or amp up charges on the existing guys. He has a couple of tax cheats in Manafort and Cohen, and lying to the corrupt FBI (Papadop and a couple others). Politically, he has lost.