Totally depends on a lot of factors:
1) How public was the incident?
2) What was the incident about (mitigating factors)?
3) How much property damage and physical harm was done?
4) Who outranked who?
5) Who threw the first or only punch?
A commander will take statements from both soldiers, weigh the evidence, and either article 15 one or both or send one or both to courts martial.
If they were busted by an NCO without doing too much damage, I just see a lot of dishwashing and lawn mowing in their future.