What happens if i do a titan with my ally, than i leave and come back and we finish it? Do i get my normal loot or just reduced?
AFAIK, to collect loot you need to have hit the titan and be there when the titan dies. If you hit the titan than leave to hit other titans, when you return your previous damage will be accounted to ex-member.
And yes, your titan loot will be reduced, which is the case when you merc and join alliances when the titan has already spawned .