All of us would mostly dead by then and tbh, a century is quite enough for one idea to decay and became a heap of trash if people lose interest in it or people no longer hopped on to the train of being interested in it. Though I highly doubt cryptocurrency itself would be dead by then but BTC itself might have some tough times ahead since you can basically say it's fighting over dominance over the coins that other countries may be creating.
It seems to me that the individuals most directly affected by the Bitcoin supply supply are mining workers.
Perhaps the miners will be forced to move away from the rewards they get in return for their work once the mining of 21 million bitcoins is reached and thus there may be no motivation for the miners to continue supporting the network.
Indeed they are. Though miners may actually be rewarded quite well if the BTC price went up more than it is right now. Chances may be close to nil but if it were to happen, I'm pretty sure miners would be more than willing to continue not to mention the possible improvement on the efficiency of mining machines. They may even be able to reduce the costs to accommodate the price so that it could still be bearable to continue mining.