With a free flowing reg, you have plenty of time to get to the surface, your cheeks might take a beating a bit...hehe Often times, it usually your backup reg that free flows from lack of use. As far as hose failure...if it is the low pressure hose bursting, depending on what you have in your tank when it happens, you can usually get up with no problem. With a high pressure hose depending on how old the hose is. A really old hose has a large ID where it screws into the reg, which means that if you blow a hose watch out it will be like bull whip, and you will have to get a hold on it before you sustain some damage. Fortunately most all in use now have a pin size hole (Safety) allowing pressure to register, but not a lot of air volume escaping, and you can still come up safely, although if you don’t have a spare hose, your dive is over.
Hope this helps, just my opinion, after 50 yrs diving.........