I would predict 18 months for this current slowdown. But it could be less or more.
I also think many of the furloughed pilots will either never return or will have found new flying jobs.
When I got hired at my current company everyone said, "There will be zero hiring at the majors for another 5+ years. Thousands upon thousands of pilots on the street." A year later Continental was hiring. Then Delta and United and UPS and FedEx snapped up our pilots. We had some go to companies which subsequently turned out not to be good choices (not the pilots' fault).
There is no crystal ball. But things are usually less bad than they look, at least depending on where you sit.
Frankly, now would not be a bad time to get into it if you want to start training. Get your certificates. Get a job instructing or flying freight or whatever to build time and experience and be ready.
18 months ago the regional carriers couldn't hire fast enough.
But it really depends upon what happens with fuel. If it spikes again we could be in deep trouble and the industry may face massive capacity cuts.
Right now fuel has leveled off and even gone down a bit. Good news for now.