The last day of 737 will come sometime soon too.
The classics have mostly or entirely been retired, with the most common models being the -700 and -800. The family has enough flexibility to evolve in range without needing a completely new family. The 737 still has its place as the short to medium haul work horse, so I don't see it going anywhere for a long time.
There are huge demand for A321LR precisely because there is a need for 757-like capacity and range. Granted, when 757 was discontinued the demand wasn't there yet.
Note that Boeing was trying to sell airlines on a clean-sheet aircraft when Airbus launched the A320neo, and _quickly_ started gaining customers, including those that had been loyal to Boeing for decades. Boeing needed something to counter the A320neo, hence the MAX had to happen—and soon.
Aviation regulations are often written in blood, and while the MAX is obviously not in a great place, it's not necessarily doomed forever. Nobody thinks twice about the batteries on a 787 anymore, or the pylon assemblies on the DC10.