I'm wondering how long will a root canal last without a crown?

Depends: How long a tooth holds up after root canal treatment depends on how much healthy tooth structure is left. If a tooth had a large filling, a fracture, and/or extensive decay, then the remaining tooth is probably thin, weak and unsupported and liable to fracture. In that case, the tooth should be restored with a crown.

Not long: The bottom line is that if you want to prevent breakage of the tooth you paid so much to have root canal treatment , you need to have a crown made for it.