Well, it's more viable than you might think. Putting a 300 degree sphere on the surface would eventually get somewhere. But getting anything useful back is pretty hard, since you'd have a probe that's boiling water below 25km of ice and probably far from the lat/lon it landed at.
I would imagine the water channel would re-freeze fairly rapidly, so you'd end up with a "bubble" of liquid water around the thing slowly melting itself down.
The ice clearly moves, as Europa's surface isn't just same as an airless, solid ball-of-rock's default: craters, but has all sorts of features that reshape the surface, so given enough time, it'll equilibrate. (What 'enough' means is left as an exercise to the reader). There are papers[1] that discuss the ice properties, but it's hard to get a specific answer out of them. There have to be tons of research papers out there about the design criteria for melt-drill probes like this, for Europa, Enceladus, and others.
Maybe the main melt probe could leave behind little RTG powered relays as it descends. They'd get frozen in place as the main probe continues melting its way down.
