What happens to reputation gained\lost from that question or answer?
When a post is deleted, it no longer counts towards your reputation: that includes both up votes and down votes.
However, reputation is cached, and any reputation changes will not reflect in your total until your reputation is manually recalculated. This can occur from:
- You manually doing it yourself by going to the reputation page and pressing the Trigger Reputation Recalc button
- A moderator or Stack Exchange employee doing it, generally as part of other action done to your account (think suspension)
- A global recalculation, usually due to some major change in how reputation is handled. This is extremely rare: once or year or less.