The business has 3 partners. (When we bought into the business a few years back, we were given shares)."
Use of the words "partners" and "shares" don't help us. Is this a partnership, a corporation, what?
"If we go out of business, can one of remaining partners sell the business without the other partners knowing about it?"
We can't know from here. Is the remaining partner the president of the corporation with authority to sell off assets? Is remaining partner the GP? What kind of by-laws, operating agreement, partnership agreement do you have and what does it say?
You own your interest until you transfer or sell it to someone else (or the partnership-company dissolves according to some predetermined date).
Sounds like you need to talk with a local corporate-business attorney.