Bitcoin's total number of coins will never be a problem. In current times the majority of the people can't even afford to buy 0.1 BTC anymore, and soon they won't be able to afford 0.05 BTC, and so forth. Bitcoin's total coin cap can be looked at from various perspectives.

21,000,000 BTC
21,000,000,000 MBTC
21,000,000,000,000 BITS
2,100,000,000,000,000 Satoshi's

Bitcoin's divisibililty is something that people tend to ignore since they just see Bitcoin's coin cap is fixed at 21 million Bitcoin's, while in reality it's just a GUI based level unit. We should accept that not everyone in the world is interested in using Bitcoin as their daily currency tool, so there will be enough coins, or better said, Satoshi's left for those who do end up using Bitcoin. In easy terms, no need to worry about this aspect.