things like "Piano's"
Can you re-use that apostrophe if you melt one of those down?
(Not very dorfy, I know, but the plural of 'piano' is 'pianos'. Or, rarely, 'piani'. That's the singular-posessive you're using there, or possibly the contraction of the definite identity phrase "piano is". I pass by a similarly annoying roadside sign, fairly often. One day I'm going to get a tin of paint of the just the right colour and stop off to correct the darn thing.)
As for molten metal strings... Theoretically, it can maintain only a
very low tightness[1]. The cross-sectional mass would also be exceedingly out of proportion under most circumstances. I'm going to guess that it'll only be able to sound out an infrasonic sound, when plucked, of a very strange character, but in the absence of any realistic scenarios I'm not even starting to plug figures into formulae to confirm my snap intuitions...
It would be a very strange instrument, though. Not necessarily hot to touch (a mercurial version could work, but probably not with glass 'tensioner ends') but probably has some technical handwavium as part of its construction.
[1] Purely as some form of surface tension between the two ends, held I-don't-know-how but possibly with suitable concave menisci/capilliary-action/vacuum-capping within tubing at either end, and either enough viscosity to hold against gravity or enough reduction of gravity[2] to not need to be so viscous.
[2] Not by buoyancy, I suspect, as the medium involved would surely over-dampen the oscilation.