RWY EXCURSION AFTER SUFFERING FROM ACFT EQUIP PROB; BRAKE FAILURE.

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LANDED NORMALLY ON RWY 24 AT ISP. WAS TOLD TO TURN OFF AT TXWY BRAVO. AS BRAKES WERE APPLIED ON RWY; ACFT BEGAN TO DRIFT TO THE L AS WE APCHED BRAVO. THIS WAS FOLLOWED BY A TOTAL FAILURE OF THE R BRAKE. NOTICING NUMEROUS ACFT ON THE ADJOINING TXWY CHARLIE; I DIDN'T WANT TO ENTER THE TXWY IN A POS OF NOT BEING ABLE TO MANEUVER PROPERLY. I USED THE R RUDDER TO TRY TO STEER BACK ONTO THE RWY. THE NOSEWHEEL STEERING WASN'T ABLE TO TURN THE ACFT SHARPLY ENOUGH; AND THE ACFT LEFT THE PAVED SURFACE AND HIT A TXWY LIGHT; AND THE TXWY SIGH. ACFT DAMAGE WAS LIMITED TO A BENT PROP TIP. NO OTHER DAMAGE TO THE ACFT IS EVIDENT. HAD THIS BRAKE FAILURE NOT OCCURRED; I BELIEVE STRONGLY THAT THIS INCIDENT WOULD NEVER HAVE HAPPENED. THE WX CONDITIONS WERE LIGHT WINDS; CLR SKIES AND EXCELLENT VISIBILITY AFTER SOME VERY BAD WX THE PREVIOUS DAYS. THIS; COUPLED WITH THE FACT IT WAS A SATURDAY MORNING; MADE THE ARPT VERY BUSY. I FEEL THAT IF I HAD ENTERED THAT BUSY TXWY IN THE MECHANICALLY DEFICIENT CONDITION I WAS IN; THE CHANGES FOR MORE SEVERE DAMAGE TO THIS AND OTHER ACFT; AS WELL AS POSSIBLE INJURY; WERE LIKELY.