Yes, otherwise is more natural but less terse.
We often write "otherwise" in mathematics:
https://arxiv.org/html/1501.05438v2#:~:text=otherwise,-%2C
https://arxiv.org/html/1302.5008v3#:~:text=otherwise
https://arxiv.org/html/1501.05438v2#:~:text=otherwise,-%2E
In fact, I think that's the most common alternative, not "else".
"or else" works too but that's still three extra characters
We often write "otherwise" in mathematics:
https://arxiv.org/html/1501.05438v2#:~:text=otherwise,-%2C
https://arxiv.org/html/1302.5008v3#:~:text=otherwise
https://arxiv.org/html/1501.05438v2#:~:text=otherwise,-%2E
In fact, I think that's the most common alternative, not "else".
"or else" works too but that's still three extra characters