Seems it was a very busy night, RAF History
15/16 March 1944
863 aircraft - 617 Lancasters, 230 Halifaxes, 16 Mosquitos - ordered to attack Stuttgart. The German fighter controller split his forces into 2 parts. The bomber force flew over France nearly as far as the Swiss frontier before turning north-east to approach Stuttgart. This delayed the German fighters contacting the bomber stream but, when the German fighters did arrive, just before the target was reached, the usual fierce combats ensued. 37 aircraft - 27 Lancasters, 10 Halifaxes - were lost, 4.3 per cent of the force. 2 of the Lancasters force-landed in Switzerland. Adverse winds delayed the opening of the attack and the same winds may have been the cause of the Pathfinder marking falling back well short of the target, despite the clear weather conditions. Some of the early bombing fell in the centre of Stuttgart but most of it fell in open country south-west of the city. The Akademie was damaged in the centre of Stuttgart and some housing was destroyed in the south-western suburbs.
140 aircraft - 94 Halifaxes, 38 Stirlings, 8 Mosquitos - attacked railway yards at Amiens. 2 Halifaxes and 1 Stirling lost.
22 Lancasters of No 5 Group to an aero-engine factory at Woippy, near Metz. 10/10ths cloud caused the attack to be abandoned before any bombs were dropped. No aircraft lost.
17 Mosquitos to 5 German targets and 10 Mosquitos to airfields in Holland, 2 RCM sorties, 11 Serrate patrols, 2 Stirlings minelaying off Texel, 31 aircraft on Resistance operations, 18 OTU sorties. 1 Serrate Mosquito lost.
Total effort for the night: 1,116 sorties, 41 aircraft (3.7 per cent) lost.
The number of sorties flown on this night was a new record.
It is very hard to question an eye witness to an event, but at 20,000' (that nearly 4miles away) at night, I begin to wonder if an eye witness could see that much detail.
Does anyone have the weather reports for that night?
From this source
http://www.lancaster-archive.com/lanc_losses mar44.pdf
ME558 shot down
LL637 shot down
LL852 FTR - failed to return.
Now here is the map.
Facts don't add up for a mid air collision involving three aircraft.
I assume the bomber stream was heading north to Stutgart.
How can ME558 which we believe to have been shot down, then collide with two other aircraft both heading in roughly the same direction one crashes 6.5km to the north (possible) and the other crashes 25 km TO THE SOUTH. (doubtful).
Yes aircraft can fly on after a collision but you might have expected some crew from LL852 to have bailed out during the 25km flight.
Does this help? Maybe check Luftwaffe records for that night as to where claims were located.