Well if there are some publishers willing to make suicide (if PS doesn't make enough money then nothing will) I guess that could happen.
Well this is just my own guess but I think once again at the start of the gen Sony will focus more on smaller games (in west indies) like they did with PS4 as they want the hardcore audience on board as soon as possible. Then after that during mid and late gen you can focus on more ''casual'' userbase.
Even if we take for granted that they won't continue to ignore Switch if PS5 proves untenable it might prove difficult. From a technology standpoint if you've been gearing up for PS5 and targeting your games there(or even PS4) then you're probably not able to re-adjust to accommodate Switch and even if you can are you going to try to jump in 6 years(or more) into the platform's life? Are you going to wait for Switch 2 in hopes that works for you?
Of course I very doubt PS5 will see enough of a decline to make it an actual issue.