Odds are the crank is shot, but you can always cross your fingers and hope for the best. The only tool needed to install a crank is a 14mm (99% of crank bolts) socket wrench. If after tightening it securely, it clicks as you ride, then it's shot and you need a new arm.

Cranks don't fall off without warning. They announce that they're loose by clicking with every revolution. If not attended to, loose cranks are rapidly destroyed as the square spindle works at the corners of the hole allowing movement that cannot be tightened away.