Remember Timurids don't start coming until around 1370-ish, so don't fret too much yet. As for providing a buffer, hardly. The mongols keep all of their full stacks at their front lines, leaving a few half-stack and/or no garrisons behind to put up a fight. By the time the Timurids arrive the Mongols, as these other guys have mentioned, have exhausted themselves leaving a nice open expanse of undefended territory for the Timurids to claim and pick up where the Mongols left off.