If you mean one of them continugin to exist, it's basically not gonna happen, languages do not stay the same over that long a period of time, especially during the time period this would happen, however if you mean a descendant language that's part of the Tocharian language family, that's more doable.
To keep one suriviving you basically need the ancient Uighur tribes to either not invade the area or for them to be less unified and have them resultingly adopt the languages.
Yes, Buddhism.Tocharian endured as a liturgical language after it had died out in everyday speech. It escapes me what their religion was (Buddhism, maybe?)