Use may yet when something is still possible right now, though the outcome is uncertain: The plan may yet work. Put yet between may and the verb: may yet win, not may win yet. If it's settled, say may have worked instead.
Which situation are you in?
Writing a forecast before anything is decided? The talks may yet produce a deal. You're speaking while the situation is open, and you're keeping both outcomes alive without committing to either.
Reassuring someone mid-crisis? Don't give up; we may yet find a way. The struggle is still going on, and you're telling them success hasn't been ruled out.
Recalling something still undecided, like a candidate who hasn't announced? She may yet run. Notice how yet attaches to future-oriented verbs like win, run, find, produce, never to events that are already finished.
Writing after the outcome is already settled? Drop yet: say the plan may have worked about last month's scheme, or she may have won about yesterday's race. May yet there would wrongly imply the ending is still open, so a settled result calls for the past-possibility form instead.