There isn't monetary deflation in bitcoin (expect for lost coins).
As a global reserve currency, bitcoin would act as an "index fund of everything". Economy is expected to grow, but it's not guaranteed. Which means that there's always a non-zero risk associated to it. There's more risk on short time scales, and less risk on long time scales.
There will be if it's successful - 90% of the bitcoins ever mined have already been mined, for bitcoin to be useful at a long term world wide level it needs to store enough value even as the size of the world economy grows - if it can't them it will become a limit on economic growth much as gold became in the last century.
So because the number of bitcoin is fixed to remain relevant bitcoin will need to continually deflate (ie increase in value) so that there's enough to represent the size of the economy
As a global reserve currency, bitcoin would act as an "index fund of everything". Economy is expected to grow, but it's not guaranteed. Which means that there's always a non-zero risk associated to it. There's more risk on short time scales, and less risk on long time scales.