I think it's too soon to let Can go. He has potential, and looked like he was coming into form towards the end of last season. As others have said Hendo isn't likely to be available for every game in a season that's going to be challenging on stamina and fitness. I'd keep him for at least one more season.
It will depend if he would be happy to be on the bench if ever we signed Keita
We have enough games coming that they will all get a decent amount of games to play.
One of our problems has been we have a good first team, but as soon as we have 1 or 2 out with injuries or suspended, we do not have the quality coming in to replace them, I like players like Lucas, but they are not the quality we need to win Championships and Cups.
Our rivals have the likes of Fabregas, Martial, Sterling & Willian coming off the bench, we need similar quality to rival them.