It would fail...
#1--Gentle fist is not meant to crush and break bones...Just close chakra points.(In part one we found out that being a Jinchuuriki is the perfect counter to this a slight flare of his chakra would undo all of the chakra sealing)
#2--a Large air palm would just push him away and in the slight chance it could damage him he has high speed regeneration.(Don't know why every one is hyping Gai so much...Madara is just screwing around with him like he did with the five Kage...Sure Gais is too fast for him...but so far has shown nothing that should permanently put him down--As a matter of fact, I doubt what Gai has done could even put down a four tailed Naruto...remember even the single tailed cloak could protect the whole alliance from Juubi sized fire Jutsu...Super Tornado's and Kirin sized lightening strikes from Juubi's Tenpenchi and Madara>4t Naruto so...