Thanks all for the insights. In the end decided to go Saturday to be more sure we would be Sunday at destination, and also the weather for the South of France for Sunday (morning) didn’t look so great (Sunday morning a SIGMET was issued for the area around Cannes, EMBD TS, SEVERE MOUNTAINS WAVES, SEVERE TURB).
So we departed Cannes Saturday at 10:23Z with a Z-Flightplan. Directly climbed to FL100 in direction of Gap (LFNA), with the plan to pick up IFR at LTP. As was seen on the weather radar some clouds and light rain could be expected after Gap. Unfortunately it was not possible to outclimb that weather without oxygen. Tops appeared to be at FL140-150, although Windy/GRAMET suggested maximum 8000ft / FL100.
Therefore a 90’ degree turn to the left was necessary to stay in VMC. As this was foreseen, plan B was to fly West, towards lower terrain, and see if we could fly below the clouds towards the North as METARS/TAFS before departure gave forecasts (M)VFR conditions along the way. Indeed, 15nm North-East of Montelimar (MTL) a nice ‘gate’ opened up abeam the Rhone in which we descended to FL80 and direction North could be resumed. From then on we would be able to descend to altitudes above 0 degrees, so we also picked up IFR and continued towards Germany. Below a small video of the weather avoidance. The video starts at the part where we just arrived above a closed layer of clouds. Maybe I should have deviated to the left before we arrived at that cloud layer as in case of an engine failure you don’t have really options left.. Let’s say you would find yourself at FL100 just above the closed cloud deck, would you continue in such mountainous terrain?
At BETEX a nice ‘direct destination’ was given. A latest weather radar update showed some rain after Düsseldorf: The ATIS from Niederrhein gave BKN014, ATIS DUS SCT030 Towering Cu, Light Showers of Rain. Then just before passing Düsseldorf we descended from ‘on top’ at FL80 (-7’C) through a thick layer of clouds to 4000 which brought us to 2’C and VMC again. To avoid possible icing we descended with 900ft/min. Eventually we descended to 2100ft (the MVA) and just after passing DUS airspace, ATC asked if we were ready to cancel IFR, because otherwise they had to give vectors to stay in 2100ft MVA area, as the MVA rises again to 3300ft after. As we were already VMC, we canceled and continued to EDLS while circumventing some local rain showers and arrived at 14.45Z 
Glad you manage it, any IMC at FL80 rings the icing bell no matter how you play around it
On +FL100 above clouds versus going bellow, I am happy to stay above clouds and take my chances on engine failures while breathing enough oxygen
My view on engine failures in IMC either 1/ you have lot of landing options bellow, so you can pick very late on IMC decent or 2/ there are no landing options bellow and IMC/VMC should not matter, a simple Bayes rule that works far better than assuming there are landing options obstructed by clouds
Low IMC engine failure is no different than EFATO on unfamiliar airfield, what’s above 500ft agl is irrelevant and sucess is function of terrain length, wing level and slow speed speed
