Mixing coolants is not a good idea and the MB coolant is specially formulated to protect the alloys and seals used throughout, but these are PROLONGED effects of use (or non-use)!
You can go merrily along for now without worrying about doing permanent damage to your engine...just get the system flushed and refilled as prudently as possible...buy enough MB coolant this time...and have the flush and refill done at the tech's expense!
2009 ML350 (84K) - Family vehicle
2001 CLK430 Cabriolet (71K) - Wife's car
2005 BMW 645CI (124K) - My daily driver
2012 Mustang V6 (60K) - Daughter's car