No doubt many of the microbes die off or go dormant, but the compost isn't totally dead. There was a thread here awhile back about a bag of commercial compost that sat in a garage for 10 years. Microbial analysis showed it was still very active.

It's generally accepted that you get the most benefit from compost when it's fresh, but it doesn't lose all its mojo in a few months, either.

if you spread it out at all then it gets very hot in the sun you'll probably kill off a lot of the MO's. But left in a pile, or put in bags/ buckets bins etc, there would probably be some gribblys still ticking along, or sitting dormant waiting for better conditions to start up again.

I agree with the other replies. Another thing to remember is that you have varities of microbes that are already in place where you intend on putting the compost. These microbes are usually the ones that live in your particular environment. They will take over in the compost material when it is added to the garden. Visualize that the compost is food for your microbes and the microbes are producing food for your plants.

Generally, although there is little good research out there to support this, the bacteria will go dormant as the amount of moisture decreases. The normal life span of most bacteria is about 30 days so they are constantly regenerating, but will shut down into a dormant state to survive when conditions are not what they need to continue living.