https://he.wikisource.org/wiki/%D7%A7%D7%98%D7%92%D7%95%D7%A8%D7%99%D7%94:%D7%91%D7%9E%D7%93%D7%91%D7%A8_%D7%95_%D7%9B but that's generally not taken as an actual obligation

My understanding (but no sources at the moment, so just a comment) is that the status and prohibitions of Nezirus extend beyond any specifically stated end-time or default 30-days until the proper Korban, etc. is completed. As a result (and this is the context where I learned it, many years ago), anyone who becomes a Nazir Bezman Hazeh (and the last almost 2,000 years) is stuck in that status until Mashiach. https://en.wikipedia.org/wiki/David_Cohen_(rabbi)

@manassehkatz that begs 2 questiona (assuming a time when sacrifices can be made): 1. If it extends in the absence of a korban, does it extend for another definite term or it just keeps going? 2. can all sacrifices be offered on any day of the year? Are there any days on the calendar when would NOT have been allowed to offer the korban required? A third question might be tangentially related -- what does someone on ir miklat do if he has to give a korban?

FYI, all based on recollection of learning these things in the past (more than just "read the Parasha" but far less than "studied relevant Gemara in-depth"): 1 - Just keeps going until Korban/etc.; 2 - Generally speaking, personal sacrifices can't be brought on Shabbos; 3 - Interesting question. Might be that they just have to wait until death of Kohen Gadol (ironically for a Korban).

@manasseh personal sacrifices with a fixed time can be brought on shabbos. The classic examples are korban pesach and the kohein gadol's daily chavitin and yom kippur par (and par helem davar). I don't think nazir is included but it's not as simple as you say.

@AA Interesting points. I don't think of Korban Pesach as personal, in the sense that everyone has to do it and it has a specific time, and it is shared by groups. But it is personal in comparison to true communal Korbanos. Kohen Gadol daily is "personal" but a specific requirement & YK Par is "almost" communal - those are specific Mitzvos Aseh Docheh Lo Taaseh like communal Korbanos, as I understand them. Par Helem Davar might be a different story - interesting example to think about.

@manasseh communal korbanot are not permitted on shabbat because of aseh doche lo taase. That principle can't be used to override shabbat laws because shabbat is both an aseh and a lo taaseh itself.