I got a pair of Prologue 6 mono-blocks plus a Dialogue Premium Preamp, driving my Focal Sopra 2 with magical sounds. Had lighting strike last year and my AV receiver was toasted, and these suckers still standing with no issues. So my money ended up going for a new receiver, instead of the initial plan of upgrading the Prologue 6 to Dialogue Premium HP mono-blocks. Will do so once I saved up some cash!
So I think you’d be more likely to change tubes more frequently due to tastes (typically tubes last more than 2 years), instead of changing these amps due to their solid reliability.