No proof will ever be enough for the fanatics. We've seen that with the indictments already done, no matter who it is there's a but but but excuse. And that's for people no one had heard of before, let alone trump.
As for the investigation, don't expect anything bad to happen to trump even though it will show that serious crimes had taken place. The aim isn't to punish trump, just show what Russian interference had taken place. The only way trump can face the punishment he deserves is if the house of reps pursue it and right now there's no chance of it.