Ideally it would be great to keep both, but likely we'll only end up with one. If we lose both, then that's not ideal but, not necessarily the end of the world.
Firstly, Ben Hunt is coming next year, a proper, premiership calibre half. Anything we lose with Widdop, I'm sure Hunt will be able to make up for. Mann and Field and even Hutch would be options to partner him. I'll hazard a guess that whoever of those 3 partner Hunt, it will likely be an upgrade on what we have today (Widdop and McCrone).
As for FB, again Mann and Field would be options. Over the last 2 weeks, our attack has actually improved having Nighty as a stock gap FB. No reason Mann or Field can't do the same. If we have to go to market, yes a guy like Michael Gordon on a 1 year deal would be ideal (and the there is a chance that Steve Marsters will be our long term FB post 2018).
No point worrying about it to be honest. So much can happen in 6-12 months and I'm sure there are more twists and turns to come. I'm just enjoying the ride this year, and the fact we may actually be premiership contenders with our current squad, when most predicted the spoon for us.