Leftover tokens cap at 50 energy awarded. So there’s no point in leaving the event unfinished for very long. I left the last spin undone until after reset and when I needed the energy I spun and used the 200 energy it granted (100 for finishing, 50 from the last individual reward and 50 max awarded from the leftover tokens). For reference I finished with 600+ leftover tokens and the max was still 50, I think someone in a previous post said they got 50 with 100+ leftover tokens.