What would happen if all sites at the same time quit subscriptions? 

shutterstock has no income

Life would go on just as it does.

Cranky MIZ
The voice of reason

subspecies feeding on subs will die out.

I don't believe they would die out per se.
Think rather they would EVOLVE.

It just might even give birth to a new life form altogether.

Cranky MIZ
The voice of reason

There would certainly be an increase in the amount of global warming.

It could also affect the atmospheric conditions on Mars, so that it began to have rainfall!

Cranky MIZ
The voice of reason