Villa, he had already won everything in his career back on his leg injury in 2011, he was 30, but still, that took him 8 months out, missed our second half os the season (it was a huge part of our UCL and Liga runs) and couldn't play the Euro 2012.
Not only missing that whole season reduced his legacy as a player at club and international levels, he was still great as a 30 y/o player, but once he came back his speed and power were affected, without that injury I think he could've played at the top level, at least, until 2016, after the injury he was still good, but had lost and edge on his game.
And then there's Sergio Asenjo, the guy was brilliant and broke through really young (19 y/o), a lot of talent, explosive, good height... but he's blown his ACL 4 times already, the first one when he was 20, back in 2009. We don't know where his ceiling was, probably could've taken over the spot for Spain after 2010 and hold it until today.
The first time Asenjo did his ACL, that opened the doors to... David De Gea, the second time he had the injury (loaned in Malaga), it prompted Atletico to look for a loan on his spot and they got... Courtois. If Asenjo managed to stay healthy, he could've kept 2 of the best GK's of this decade warming the bench.