I've never been to Inle Lake or Heho, and never taken a domestic flight in Myanmar, but I would be worried about missing my flight home on both of your options.

How about this:
Day 1 - Arrive Yangon in the morning from BKK, SIN or HKG, afternoon flight to Bagan (not sure if this exists)
Day 2 - Bagan
Day 3 - afternoon flight to Yangon
Day 4 - Yangon
Day 5 - Yangon, evening departure


Ideally you add an extra day and spend an extra day in Bagan