Fernando Muslera,I remember him from the times he played at Lazio where he excelled for some time or any other Serie A team don't recall that well now.What I know is that he is truly a great goalkeeper and I think the best option for Galatasaray is to keep him until the end of his contract.
Muslera is not only a good goalkeeper, he is also a very good professional. There is hardly any football fan in Turkey who does not respect Muslera. Even Beşiktaş or Fenerbahçe fans respect him because he is a true professional on and off the field.
I don't know if the other goalkeepers are useless or not in the team but where I live we have a law that the goalkeepers,young ones should only be trained by the team goalkeeper so if they are young Muslera can be a great teacher for them thus improving their performance and Galatasaray does not need to spend any more money to buy a new one.
Galatasaray tried something similar with Tafarel before. Tafarel and Muslera did not play together, but Tafarel was Muslera's goalkeeper coach for a long time. When the time comes, Muslera leaves football at Galatasaray, goes on vacation to his country for a few years, and then works as a goalkeeper coach at Galatasaray. :)