50 miles is not a big deal, unless you are climbing mountains with a load.

On my road, go-fast bike (no baggage), I could do 50 miles in 2-3 hours, assuming flat or small hills and not much headwind.

On my loaded touring bike, it would probably take me 4+ hours, but I can carry 50+ lbs of gear.

Off pavement, you will probably average 10 mph or less (unless it's all downhill).

As said before, it depends on terrain, road surface, headwinds, but if you are trying to get an idea of whether a bike is a feasible bug out vehicle, then yes, it absolutely can be.

Greg