if you fly long enough you will probably have an engine failure eventually.
The above is clearly true, but how many of us spend their entire airborne time orbiting over the centre of London at 2000ft, or flying above the N Sea with surface winds of 50kt?
Not many.
On most flights, there is a time window during which an engine failure is going to result in a non survivable crash (unless you get really lucky). There are many airports where the approaches are like that. But the chance of the engine packing up right during one of those slots is very small. I reckon that on a typical flight around UK or Europe one spends maybe 1% of one's airborne time in such spots.
I have flown straight over the Alps a number of times. Looking at the terrain below, there are ample landing sites. There are huge valleys but there are also smaller spots where one could put down (not ever get the plane out again though). Flying high will help greatly with the options, but one may need an IR for this.
Doing the above above an overcast is something else but I still do it. Run a GPS with a large topo map on it, showing the valleys to glide into, and fly as high as possible - 10,000ft or so above the terrain.
I would consider flying over a forest much more risky. The plane virtually always ends up totally wrecked and survival seems a matter of mostly luck.
If you have the option, always try to have an escape route.
Absolutely right. And most of the time one does have one, or can easily arrange the route (if VFR) for it to be so. The only time I see myself having no escape route is when taking off or landing at some airports, or flying over dense forests. Mountains usually have options, and for water one carries a life raft.
Finally, look after your engine. Looking at maintenance and operating practices it is obvious there is a vast spectrum of reliabilities, even across the same engine type. I have just seen a dreadful fatal accident report in which the engine was seriously knackered internally, and not making its rated power. This kind of thing is avoidable simply by cutting open the oil filter at each oil change and checking it for chunks of metal, sending off oil samples for analysis, and making sure the engine makes the rated RPM (or fuel flow/MP if VP prop) on takeoff.