Team elected arbitration doesn't prevent a player from signing an offer sheet, it just puts a deadline on it (July 5th in previous years).
Doing so is an option to prevent negotiations from dragging on through the summer months, but it's a bad faith move that will just further divide their interests.
It's a last resort to gain leverage that also eliminates any possibility of cooperation moving forward.

Winnipeg would be backing themselves into a corner. Trade him by July 5th or you're stuck with him and if he was even a little bit open to staying before, that door is slammed shut.
They do not want a deadline or trade restriction if they are hoping to extract good value from a trade.

Side note, Dubois reportedly attended the draft in Montreal with the belief a trade was in the works but it fell through, so Hughes went with Dach.
Whatever Winnipeg wanted at the time, Hughes was not willing to relinquish. He's not going to cave to trade pressure now if he wasn't willing to do it in Montreal a year earlier on home turf.

Regardless of what happens, I don't see Dubois being a Jet this time next year. If he is, the only possible redemption is no less than a cup.

does it mean he would only have 5 days to sign one? from july first to july fifth? i guess i got mixed up in the dates. as for the arbitration, i think the cooperation between dubois and jets is pretty much over. espacially the way the year ended for wpg.

i did not know that rumor about dubois and Mtl draft, interesting!

Not sure of the exact dates due to the schedule modifications in recent years, but that should be correct this season, July 1st-5th for offer sheet window prior to arbitration filings.

As for the relationship ending, there's always a possibility.
Winnipeg could offer Dubois $11M with full NMC for 8 years and build the team around him with a top role while unloading people he may not want to play with and bringing in some he does.
Players can often be convinced, it's just a matter of how much it takes.