The answer is actually infinite.

This is because there is no limitation to the maximum number of runs scored in a single ball. A batsman can run for how much ever he could. Even if there were no overthrows, he might be capable of running 4 runs or even 5(think of him as Usain Bolt…), or the fielder may be too slow to run after the ball and retrieve it in time.

We can never be sure how much runs he could score. According to theory, like NitinGurbani has said, it is 1653 runs. But  we can’t be exactly sure.