If the need were to arise, we could add one or more decimal places and work in fractions of satoshis. If we wanted we could even give it a name like 1 satoshi = 10 "finneys" (named after the late great Hal Finney). At some point in the past, people in the US used "mills" where 10 mills = one penny. Eventually people stopped using mills because 1/10 of a penny just wasn't worth the effort; but nothing fundamental changed when that happened. (The monetary base M_0 didn't suddenly change when we dropped the mill, for example.)

https://en.wikipedia.org/wiki/Mill_(currency)

EDIT: If someone were to suggest we change the 21 million bitcoin cap, basically everyone would oppose that. Once you pick a cap you have to stick with it. But if someone suggested adding an extra decimal place like in my 10 finneys = 1 satoshi example, that wouldn't be nearly such a big deal. Just like using versus not using the mill is not a major issue.