It's hard to say what "crucial to making it happen" means. Like he was involved in the counter attacks that led to Sigurdsson's goal vs United and Richarlison's vs Brighton but did he do something that a large amount of wingers couldn't have done? I'd say no he played a simple pass and our better players made something happen. There's a video posted on here of all his "moments" from the season. Go and watch it and pay attention to where on the field most of the stuff he does happens. Almost the whole video is 40 yards or more from goal. There are barely any touches or passes into the box. This is a problem for a forward.
As for the who should he be replaced with I've argued and will continue to argue that I'd rather sacrifice a bit of work rate and midfield link up for the in and around the box ability of Lookman and possibly Onyekuru. But basically any other winger we've been tentatively linked with, Malcom, Neres, Under or whoever else, would probably be an improvement.
And as I said I'd be happy to be proved wrong and for him to be a player that suddenly is capable of being a constant threat. But I just didn't even see that many glimpses last year. His best ability in attack was setting up Digne which is more about how good Digne was at movement and crossing than Bernard being some kind of brilliant attacker.