For those on foot marching, any areas of sand will be a tough slog. Slows you down and is far more tiring.
Absolutely nobody is getting out on foot, not with the nearest point of vague safety 40-50km away and the British in control of the road.Chances are, many never even bother trying, or give up after a couple of miles and turn back, or drop down and wait for the British.
The only reason anyone would even try to get away on foot is if they think there's a chance of getting to an assembly area to hitch a lift on a retreating column before it pulls out. As soon as it's clear that they're cut off and without transport any remaining foot soldiers will surrender (and if necessary, go looking for some British troops to surrender to - dying of thirst in the desert is pointless). The only possible exception is sacrifice rearguard units trying to delay the pursuit - and they'll surrender once they're bypassed, overrun or out of ammo.
The 5th Light and 15th Panzer Divisions are fully-motorised units, so the only German troops in this situation will be stragglers who've lost their transport. I'm not sure about the Italians, but any non-motorized units in the Trento division probably surrendered as soon as the defence at Nofilia collapsed and certainly would have when they learned that the Germans had failed to break the roadblock and no relief was available.