It doesn't look like the vis was that bad whereas G-LBAL was in fog at night with no experience of an IF towering take off.
SAR modes really aren't suitable for over land work and if the weather had been that bad where they took off, I am sure they wouldn't have bothered. The SAR hover mode on the 139 - if it was fitted on this one, might have been an alternative to groping in the whiteout but we don't know if it was available.
Mountain conditions change so quickly that it is easy to get caught out and I think they launched in OK vis/cloudbase but were cut off from their escape route into clear air/lower ground - it happens unfortunately and what looks like a viable escape can quickly become a trap.
These guys were presumably SAR trained and mountain qualified?
For the IF option I suspect their MSA would have been upwards of 10,000 ft in the Alps at well below zero in icing conditions so really not an option at all.