I have not pontificated tubes will go away -- but I will GUARANTEE the "majority" of users 20 years from now will use software (or who knows what NEW tech will be around then?) as the tech improves and the price void between digital and tube amps widens and widens ..... you will see more converts....and as said some of the very young and up and coming beginning pros might never even own an amp
But take heart---there are still record players......
there are still tube radio users and HI FI tube audio lovers --- Im sure there are still people using VHS video players...... but -- all those have gone from " everyone" using them to small "niche" markets. Personally I see tube amps going the same way.
I have 6 grand kids --- Digital, phone-- google-- tablet-- is the IMMEDIATE go to .... period
Wanna have some fun ???? Find any 20something year old ... give them directions in "go 2 miles North -- turn WEST on hwy 4 " etc etc -- as soon as you say GO NORTH they will get a confused look and the rest .... you might as well be speaking Mandarin..................