You'd be still able to solo stuff without reforging everything to expertise thought
.
Zon'ozz = Killed 6 secs after enrage
Al'akir (heroic) = Killed 5 secs after enrage
Occu'thar = Killed 3 secs after enrage
LK 25H = Killed when about to enrage
Baleroc = Killed 0.5 secs before enrage
Maloriak = Killed 9 secs before enrage
Morchok = Killed 12 secs before enrage
Cho'gall = Killed 21 secs before enrage
Shannox = Killed 30 secs before enrage
Yor'sahj = Killed 48 secs before enrage
Chimaeron = Killed 55 secs before enrage
So yeh, that expertise is definitely needed