I am not sure what is your concern. I assume you are talking about the rubber grips on most of the current 629s?
The traditional 29 and 629 came with the nice Magna Grips, nice looking and deep checkering. About 50 rounds would eat the skin out of your palm. Most people replaced them with the Hogue finger grove grips, which let you keep hold of the gun when firing top end loads. They are just plain plastic, like these on this gun from Cabelas. All of the new entry level Smith and Wessons come with a version of those, the fine wood grips are extra and usually from the Custom Shop.
The normal model 629 they now call the Classic. With the wooden grips and nice polish they will cost over $200 more than the current dull finish guns. Actually the older guns came with nicer grips than those shown on the SW web site.
Except for the hammer nipple in the older guns, there is nothing to break on a typical model 629. The red ramp from sight might fall out but no real loss, replacements are everywhere. I collect Smith and Wessons and have some over 100 years old and never had a spring wear completely out. You can shoot them loose and need end shake shims if you shoot enough magnum loads.
As far as grips, I do not consider Smith and Wesson factory grips a top of the line product at all, there are dozens of companies that can make a custom grip for any of the Smith and Wesson revolvers. I have factory grips I have taken off of several to customize or a couple I have add Crimson Trace Laser grips for walking out in the dark in bear country. Other than that, I cannot think of any parts that I worry about.
There are some guns, like a single action army that have springs that will fail over time, but not the wheel guns. Same with Ruger, I have never had a Ruger wheel gun, SA or DA have a part that failed. Guess that is why so many people trust them.
My only SW in 44 mag is the model 29 from 1981, it came with the big walnut grips, target trigger, target hammer and all in a wooden display box. None of that applies to the off the shelf guns anymore.
If there is something about the newer versions that are failing, I would sure like to know the source of your concern. Some guns like 1911s and ARs, I do see the need for spare parts, buy them, and keep them handy. Just saying. Enjoy your 629, not much finer a gun on the planet.
Forgot the names but a survey was once done among gun writers and they were to choose only one handgun and that was all they could have for life. Some said a 357 SW, which would be me, one went with some 22, a Ruger semi auto I think, but several chose the model 29/44 mag Smith and Wesson. The reason was, it would defend the home against anything, it could be used to hunt deer, defend against bears, snake shot for snakes and 44 specials for rabbits and squirrels.
I have carried the model 29 four inch a million miles on the belt is seems, it is not much for concealing, but if there is a threat, and I did face a bear at 3 am once, there is no better handgun to be in your hand.
Enjoy that big guy.