I don't particularly disagree with anything you say, a4fly, but you are assuming certain things which may be true but which we don't actually know.
I guess you are assuming he was flying VFR and then inadvertently entered IMC. OK, that kills loads of pilots, and if this pilot was a novice then it would be a open and shut case of "here goes another", another useful slide for the CAA safety seminar, etc.
While I am not going to write anything here which amounts to inside knowledge, and commendably neither has anybody else, yet, this pilot was not a novice. You can also look him up on the FAA database: he was instrument rated, PPL/ME.
This doesn't rule out the possibility of it indeed being a simple explanation like the above, but it makes it a lot less likely.
In normal GA operations, it isn't so much the "survivability" of the situation that is in issue. It is not getting anywhere near it in the first place. A flight like this would have been done IFR/airways, with oxygen, in VMC, or not at all. Often, there is a VFR "on the deck" option when the IFR one is closed due to very high or nasty IMC at/above airway MEAs, but this isn't feasible over this kind of terrain. One should be at FL150 or whatever, and making weather avoidance decisions from tens of miles back, while still in sunshine.
A bit of a mystery, really.
Many twin pilots choose to fly VFR to avoid Eurocontrol enroute charges, but a Seneca can be certified at 1999kg. However, VFR is pretty useless for frequent European travel which this man was doing, by all accounts.
The issues with engine failures are a redherring. Single engine pilots accept engine failure as a risk and live with it. If they didn't nobody would fly a SEP over water, over mountains, over forests (unless it's a Cirrus). In return they get the performance of a twin but with about half the running cost, and probably well under half the maintenance cost of an old twin.