Deleted my ISO, game no longer loads, is that why?

[Dakliq3]

It's basically in the subject. I did a big cleanse of my PC a while back getting rid of anything I thought was useless. After taking some time off from P99 I was looking to hop back in but the game no longer loads. I can provide more details at a later point, but in general, is the ISO program needed to continue playing the game after the original download?

Thanks in advance!