[jaawn]

within roughly 5 years or so (very rough guess on my part), all of the available Bitcoin will have been mined. At that point, the mining part of the equation will be moot, leaving only the blockchain infrastructure to consider. Note that this may not hold true for various "forks" of the bitcoin blockchain, or for other cryptocurrencies.

[alethiophile]

Not true at all. The security of the bitcoin blockchain is fundamentally based on mining; after the inflation schedule runs low enough that it's not the major component of mining rewards (which won't be for decades), miners will continue mining, but for the transaction fees instead.

[paulgb]

No need to guess, the reward schedule is written into Bitcoin:

https://bitcoin.stackexchange.com/a/162