Does the IRS force you to pay back taxes on your capital gains? If so, at what rate? Are there late fees? Criminal penalties? How does the presence of a medical emergency or other valid reason to abort act 60 influence this?
What would happen if you decide to leave before the required 3 years of residency?
The three year rule only applies if you use the year of the move exception. Much easier to establish residency on or before Jan 1 of the first tax year you’ll file as a PR resident for.
If you did fail to meet the 3 year stay requirement, you’d want to amend all possible tax returns to reflect your new lack of BFR status in the year of the move, pay the appropriate back taxes + late fees (some % per time late),. I believe there aren’t many exceptions that aren’t already accounted for in the residency requirements (natural disaster, etc)