regardless of Bannerlord, the game Warband will still be around for as long as you want it to be. We are still playing games from the 90s
, and even Steam has a big collection of games from 90s/early 2000s.
if you can't run Bannerlord for some reason (unlikely, unless your PC is 4+ years old) and the budget doesn't permit a upgrade... then wait one or two years. By then you can buy a PC to run the game for cheap. Also consider buying a used PC, you can probably find one that will run Bannerlord for 100-200 bucks in any region.
lets say you need $1000 to buy a Bannerlord PC in xmas 2017. Same computer (specs) in 2019 will go for 20-30% of that cost.