Life sometimes hits us with a curve ball.
Sometimes, just for a wee while, we can't focus on two goals at once. Perhaps just for a week, your goal is grief. Properly mourn the passing of your best friend. Forget about weight right now - if you can't do both then don't even try. Just for ONE week. You won't gain those 2/3rds of all that excess weight all back on again - not in one week.
And then, at the end of that week, having appropriately said goodbye (even though it never stops hurting and won't necessarily feel much better by then), you can start again even if it's just purely with tracking. Just track. Then when you're tracking you can see what kind of changes you want to make.
I think your doggie probably loved you and thought you were just the most awesome person to be around. Honour him/her - be awesome. Awesome people take charge and do the right things and they find a way (even if you give yourself a week to grieve first) to work towards goals they have and eventually achieve them.
Having lost both a dog and a cat in the last couple of years I understand your pain. Please take the time to deal with this loss properly without giving yourself a guilt complex over your weight at this particular moment. Take life's curve ball and just deal with the ball itself ... just for now. You can still be a great healthy person and make good positive food choices, even if you take a few more days to feel completely ready to do that again. Don't beat yourself up. Grieve. Get on with it.
Deb, in New Zealand