Hi everyone,

I became exclusive at IS about 10 months ago, but due to high sales and incomes from PP royalties from Thinkstock with only 2500 images, I didn't quit the PP option.
From month to month income and DLs from Thinkstock have been reducing, from around 1000 DL monthly down to 350 nowadays, along with reduced income from PP royalties.

I wonder, and kindly ask for opinion from other exclusives - will my regular iS/getty/subs DLs increase (and hopefully rise) if I cancel Thinkstock partner program?

Maybe I'm wrong, but I thought Thinkstock was mandatory for everyone?

Nope.
If you are exclusive, any files you had in before Subs started can stay in or you can get them out.
If you are exclusive, there's no way (since subs) you can get any new files into TS, even if you want to have them there.

And PP cancellation is one-way, irreversible process.

So - contributor cannot change mind if sees that cancelling PP is not such good idea

In my case, and I guess in case of many other hard-working exclusives, subs are taking bigger and bigger proportion in earnings and DLs. 
More or less, the same thing is with regular DLs - no big surprises at the end of the month, positive or negative.
On the other hand PPs are falling. As non-exclusive I used to have about 40-50 PP DL per working day, now it hardly reaches 15, but still, at the end of the month, PP contributes with 150-200$.

I am curious if PP amount will be replaced from some other source, such as subs or getty or even from regular IS DLs (not in number of DL of course, but in the $ amount)

If a buyer is shopping on Thinkstock is it likely that, not seeing your images, they will go back to IS to find them? If the answer is yes you might see a benefit from pulling out of PP, otherwise you're down whatever you get for 350 monthly downloads.