i wouldn't be so worried about him, he's risen from the bottom once, he can certainly do it again. The bottom is quite high though. How many cyclist would love to have their top where his bottom has been so far. However, to me it looks like they gambled a little bit with his form timing and the virus got unfortunately the timing better of them. If it was slovak politics, someone would say Lefevre sneezed on his breakfast
They(Bora) needed for Sagan to dig deep in the tirreno, however he only could do it only on half gas, they even shortened one stage for him

. And after tirreno, there were only one day races. One can hardly be surprised, that his form is "low" in Sagan measures, where he practically has 4 full speed racedays this year. You can't count the january exhibitions.
However, even without the virus they could have miscalculated little bit. Stybar was probably one or two weaks early, sagan might have it the other way.
If sagan doesn't win nothing serious this year apart the green, then worries might be open, if he will be able to return in 2020, because if not, he might end his carrier, but it's to soon for that. For all we know, he may find his day in roubaix and then confirm it in the Amstel, and everything will be ok again. If we read the discussion from year ago, we would find the very same questions, his shape is bad, good overall, but not the beast he used to be, and then he drove everybody of his wheel in roubaix.