Had Fredo not betrayed Michael and told about Roth/Ola's proposal to him, would Michael have given Fredo something important to keep him close?

Never.

I agree, Blib.

Thank you SB.

Anytime, sweetie!

Since Michael told Tom that Fredo was "weak and stupid"--and that was before he knew Fredo was plotting with Roth--it's unlikely that he would have given Fredo anything important. But he might have listened more attentively if Fredo had tipped him, and then asked for something somewhat more important than running a brothel or a Mickey Mouse nightclub. I base this on the fact that Michael was wary of Fredo after he sided with Moe Green in GF. Perhaps Fredo's revelation of the Roth plot would have raised him somewhat in Michael's estimation.

Running mickey mouse night clubs and picking people up at the airport was big time work for Fredo, especially when he was hung over.

Difficult to fathom this question. We'd be talking about Fredo all of a sudden having an awakening and gaining intelligence.

It is hard to fathom this question. I don't think anything could have happened. After the Moe Greene comment in I, Fredo was on Michael's s**t. I could see (hypothetical) dialogue like this:

MICHAEL: Fredo just informed me that Johnny Ola and Hyman Roth are conspiring against me.

AL: Fredo said this?

MICHAEL (nods): Perhaps he took what I told him in Las Vegas to heart. You had left the room, but he took sides with Moe Greene when we were trying to get his casino I told him "never take sides against the family again."

AL: Does this show any sign that he might eventually one day...you know...be able to take something more important in the family.

MICHAEL (shakes his head): I do not know. This is a start, but...

I think Michael would have kept Fredo closer and perhaps summoned up some brotherly warmth to make Fredo feel more important and valued but it would have taken more than that to make Michael reevaluate his estimate of Fredo's value.