As I said in the other thread, selling him would be very stupid.
Can's 4 years younger than Henderson, and already at his level. He still has a lot of development in him, and in 1-2 years, he could very well be world class.
He has every attribute - power, technique, passing and competitive spirit.
Most CMs take till about 24-25 to peak. Henderson took that much time. As did Matic. As did Kante.
He's proven in his time that given a sustained run, he can be very very good (later third of this season, and the Europa League run last season). What he needs to work on is fitness and consistency. I'm pretty sure that's not very far away.
And the idea of replacing him with Keita is just weird.
Firstly, Keita is more offensive minded than Can, so if anything he should be replacing Wijnaldum and partnering Can instead of replacing him.
Secondly, Keita may well be good, but he's still only 21. Are we seriously going to get rid of someone who's been here for 3 years, has Premiership experience, and is on the cusp of being very very good, and pin our hopes on a 21 year old who's never played in England?