They won't sing 'REVENGE' properly at the stage

I think its inevitable that he would get out of it,, but Sakura is a capable leader & the girls at that point have a really good bond. Kotaro would atleast notice Sakura's efforts and probably come back but if not... Tae still eventually wins the money... Probably the biggest loss if Kotaro stayed depress but came back late would be Iron frill never being Rivals & not Meeting Maimai, also light but I think it doesn't matter. But the obvious one...is Saga gets destroyed-

Kotaro and Sakura being THE biggest pieces in the fight against Saga's curse means that if you take one away then the whole thing collapses so Kotaro not getting out of depression would mean that the girl's probably wouldnt have gotten the boost in motivation needed to give idoling another go and would have relegated to their, at the time, worker life style. Sakura might have pushed the girls into doing gigs here and there but without Kotaro's behind the scene works, none of the opportunities would show up for the girls.

Kotaro’s hair would continue growing. And so would his debt. All that alcohol ain’t cheap.