Camt swear it doesnt have a body count limit, but on my rig on max uktra settings, never ran into one.
All bodies in non settlement locations decayed only after time, not body count. Time was reasonably long - enough i coild fast travel back and forth multiple times to finish fully looting if i desired without a simgke corpse decaying. This has been true for me at least in every exterior and interior location that was not within or near settmemt borders.
Bodies in or near settlement borders - all bets are off. For me, sometimes they decay over time, sometime never - forcing me to use console commands (markfordelete) to rid myself of the bodies.