You want to save the mycorrhizae? i believe i read recently that it is fairly fragile but i would imagine some of it would survive.
However.... just a suspicion... because it happened to me before..... might this "mycorrhizae" not be fungus? if it looks like filaments and long threads.... then it probably is mycorrhizae. But if it looks compact... maybe granular a little. it maybe some anaerobic bacteria growing in the high nitrogen compact
compost area.
spreading some leaves over won't hurt mycorrhizae and dead mycorrhizae won't hurt your soil. SO... you are okay... but the fungus may or may not be. Don't sweat it. But yeah... covering it next time is a good step too.