I have this theory that Dumbledore fixed Hagrid's wand with the Elder Wand and then concealed it in the pink umbrella.

First, in SS/PS, Hagrid said he still has the pieces of his old wand and it was snapped in his third year. We know that the pieces are in the umbrella.

In CoS, Ron's wand breaks after it was hit by the Whomping Willow and it never worked correctly again. His wand wasn't nearly as broken as Hagrid's was.

Hagrid doesn't perform spells very well and this is often associated with his lack of schooling. But Harry and the others could perform a variety of spells in their third year and perform them well. Hagrid does perform certain spells fine (moving the boats to the castle, making a fire at the hut on the rock, etc.) and others he doesn't (transfiguring Dudley into a pig). Human transfiguration is very advanced and it's doubtful that Hagrid would be able to successfully do it given his education, not even factoring in his wand.

I highly doubt that two broken pieces of a wand would be able to perform any magic, especially since Harry's snapped wand in DH wouldn't work. We know now that Dumbledore had the Elder Wand and I think he might have fixed Hagrid's wand with it.

It seems like a very Dumbledore thing to do. Going against what the school governors voted to do (expel Hagrid and snap his wand).

I've heard that theory before and I can't help but agree with it. We saw in DH that the Elder Wand caused Harry's wand to go completely back to normal and yes since Hagrid was actually innocent even though really no one would believe him or Dumbledore then I think Dumbledore would feel that it was the right thing to do since no one was snapping Tom Riddle's wand in half.

I've never heard that theory before but now that I think about it, I could definitely could be true.

I have never heard of that before.
but hearing it now. makes me think that it might be true.

ooo, never heard that but it's very clever. there's a good possibility that it's true.