It's happened. Maybe the most improbable NFL play I've seen was about 20 yrs ago. Green Bay kicker Chester Marcol had a FG blocked. The ball lands directly in his chest and he runs for a TD.
The WEIRDER aspect of the blocked FG rule is that if you kick on 3RD DOWN and recover a blocked FG behind the line of scrimmage, you RETAIN possession. Happened in OT of Cle/Pit game last year. Garbage technicality that defeats the spirit of the rule.