No wonder Thor still had the confidence to save the remaining people even after Hela crushed his hammer.
With Gungnir, Luke and Dr. Banner's help, his chances of success were very high.
Luke's heart jumped when he heard that.
Loki had pretended to be Odin with the Gungnir spear for years. There probably wasn't some sort of prohibition on it that prevented other people from picking it up — at least, it wouldn't be as strict as the prohibition on Mjölnir.
Now that Odin was dead, even if Luke 'forcefully' used Gungnir like he had with Mjölnir, there would be no more issues.
It had to be pointed out that Thor's One-Handed Hammer Proficiency was an Advanced ability, while he was at most at the Elementary level with a spear.
Luke's Cold Weapon Proficiency was close to the Intermediate level, and he was pretty good with a spear.
When Luke 'borrowed' it in an emergency, would Thor be able to snatch it back on the spot?