If Smeagol had not died...?

[Tuor in Gondolin]

I think one must defer to Gandalf on the chance of Gollum being redeemed.

I have not much hope that Gollum can be cured before he dies, but there is a chance of it. And he is bound up with the fate of the Ring. My heart tells me that he has some part to play yet, for good or ill, before the end; and when that comes, the pity of Bilbo may rule the fate of many.

And to be redeemed he probably would need to live for a period of time to be
really healed, although most likely in the Shire, not Aman.
However, the Professor's theorizing on an alternate Gollum may be of
some value and not require a post-Ring long-lived Gollum

In Letters # 246 (September, 1963)
(If Sam had had pity on Gollum)

The course of the entry into Mordor and the struggle to reach
Mount Doom would have been different, and so would the ending. The
interest would have shifted to Gollum, I think, and the battle that would
have gone on between his repentance and his new love on one side and
the Ring. Though the love would have been strengthened daily it could not
have wrested the mastery from the Ring. I think that in some queer twisted
and pitiable way Gollum would have tried (not maybe with conscious design)
to o satisfy both. Certainly at some point not long before the end he would
have stolen the Ring or taken it by violence (as in the actual Tale). But
'possession' satisfied, I think he would then have sacrificed himself for
Frodo's sake and voluntarily have cast himself into the fiery abyss.