"What would happen?" On a good day, nothing as you say.
However, it takes little to strike a tube. In dry conditions the static generated by lightly brushing the tube can do it. You can start a fitting with failed starter that way. Also a transient on the supply could easily exceed strike voltage.
If a tube strikes with no ballast it is virtually a short so the breaker trips. I imagine the glass could shatter though I've never seen that. The energy dispersed will be a function of the breaker characteristics.
That makes sense, forgot how easy it is to start such a lamp! And yes, of course, a started lamp is a dead short! That's what the ballast does, limits the lamp current.
Aldi sold a rather interesting LED bulb recently, 230 V ES 27 "corn cob" style enclosed in a real pearl glass bulb, almost impossible to tell apart from an incandescent and the same size and shape too! This is the only LED bulb I've ever seen that won't cause any trouble fitting into existing fixtures and since there's no white plastic base light dispersion is very even.
