Guess it would depend if the suit stays airtight and whether the body is getting sunlight.
If the suit loses air, the remains would probably get freeze dried, if the suit stays intact, microbes would probably take over.
Was curious, found this:
https://www.reddit.com/r/AskScienceDiscussion/comments/81k1em/if_a_human_body_was_sealed_in_an_air_tight