The rumour probably stems from Flybe's recent relationship with Monarch engineering who are now responsible for maintenance on Flybe aircraft at MAN, BHX and LGW.
As part of Flybe's restructure it was suggested their aviation services division would be sold off. Engineers upset that their colleagues had been outsourced to Monarch started believing Monarch would buy the hangar but this has no supporting evidence.
Monarch has no base in the Southwest and unless they were prepared to purchase the hangar mainly for external party maintenance then it would not be of any benefit. With such a large investment by Monarch in their hangars at BHX where the runway is longer than EXT I think this rumour can be put to bed.