I have had a similar scenario twice , first time was a 2 point mulie , I held it down (like a steer) while I took my 3" folding oldtimer knife out of my jeans and cut its throat.
2nd time was a 4 point WT and I was able to run up to it (in deep snow but it turned to fight so I waited till it turned away and put the barrel about a foot from the back of its head and Blammo !
I should add , Now that I am older (& wiser ?) I would just put one in the brain every time