Information on FLR(O)

I need some information regarding FLR(o). My visa expires expires on 25th august. i'm waiting for TIER 2 visa COS from my employer. Unfortunately he ran out of allocations due to his own mistake. One COS was generated and withdrawn due to a mistake. My employer requested for another allocation with helpdesk by mentioning about my visa expiry date on 15th august 2015 still havent received any reply yet. So, basically i'm running out of time. Can you please suggest me whether FLR(O) is the right choice or overstaying and becoming illegal ultil COS gets sorted? if you know any other possible routes .

many thanks.

FLR (O) and variation is the best choice.