What is his bubba? If it's not a pacifier let him have it. Even many adults need something to help them feel more secure. My daughter still has her stuffed bunny sitting on her bed and she's 30. It's not a security item any more. It's a reminder of pleasant things. Your son will outgrow it, as Allison H. suggests. I also like her suggestion, if it's a pacifier, to let him choose something else to use as a security item.
Most of all I suggest that you be sympathetic with him. Be firm while saying, he's gone but say it with a sympathetic voice. This is a loss which he will have to grieve. You can teach him that he can have other things to help him sleep, by taking him to the store to pick out another thing.
I also suggest that you may be trying too hard to satisfy him, hoping to convince him that it's alright to be without bubba. That may be what is making him more resistant to sleep. He feels, on some level, that you're uncertain about his ability to accept that he's gone. Otherwise why are you trying so hard to help him? A brief, "I'm sorry that bubby is gone. I know it's hard for you. I trust that you can find other ways to get to sleep." period say it once and walk out of the room.
Return after a few minutes, to rub his back, pat him,or physically soothe him but don't talk with him unless it's to say, "I know this is hard for you. You will be OK."
When you say that Bubba is on the moon helping other babies you're telling him that he doesn't need bubba and/or that bubba doesn't want him. I suggest being honest with him about why bubba is gone.
I like the idea of building up to removing an item by talking with the baby/child about a story in which the item is going to help other children, etc. But he wasn't a part of that plan. All he knows is that bubba left and he didn't even get to say good bye.
He's angry with you for taking away bubba. This is a normal reaction.
Babies bond with objects. Doing so is a part of how we learn about object consistency and trust. It sounds like he's especially dependent on bubba. This is a good thing. It shows that he does bond and that his bonds are strong.
Not knowing what bubba is, I suggest that you bring him back for a visit and start over, being open and honest with your little one and involve him with him going away. Your description makes me think that this is a more serious issue for your son than it is for many children. Along the way, find a substitute for bubba to help him feel more secure.
If bubba is a bottle, you can put water in it. I'm guessing your son is around 2. If he doesn't have dental issues you should take the time to help your son let go of the bottle. A bottle has a double meaning in feeling secure. It provides something for him to hold onto but it also represents food and mom. If you held him while feeding him, that bottle helped him to bond with you.
Cold turkey works for some kids but obviously not for yours. He needs his bubba or something else for security.