However the 737Max is the last version of the 737. 737 users will have to transition away from this type in the medium term future. The current troubles force them to think hard about whether they will trust Boeing at that point or decide to go with a competing product. Of which there will be roughly half a dozen by that time.
It gets even worse, if we look at the big picture. The 787, 747-8i and 737Max have all been expensive disappointments for the airlines that ordered them. Boeing has been losing market share to Airbus for decades now, this really isn't a good trend for them. That doesn't mean that Boeing will not find a certain level of success with their next airplanes, but the damage their brand has suffered does hurt their bottom line quite severely.
Also, what? The 787, for all of its faults, has been extremely well received. The 747-8i was only ordered in small numbers because nobody wanted a quad jumbo (same reason the A380 is ending production) — the freight variant (8F) has been pretty popular (again for a niche market).
The whole problem here is that Boeing has absorbed all their former US based competitors in the past decades and has only Airbus left as a main competitor and a few much smaller ones based in Russia, China, Japan, etc. This is a unhealthy situation for the market and for the US. It was fine when Boeing was cranking out innovative products that were clearly better but they seem to have a hard time keeping up with competition and are too dependent on government support currently. Easy fix: cut back that support a little.
IMHO the 737 Max thing will probably blow over once Boeing implements some relatively simple technical changes. People seem to obsess over a lot of technical details with sensors and software processes. That criticism is well deserved but probably relatively easy to address by Boeing as well.
The bottom line is that once they get their solution past certification, that will be the end of it. Their branding has obviously suffered and this is impacting short term sales and revenue. They'll probably have to do some rebranding and maybe ditch the 737 Max brand in favor for a new version. After that, it's likely back to business as usual. Short term this just means awesome deals for carriers brave enough to talk to their sales right now.