I would look at it like any transition that has both + and - feelings, gain and loss( haha), and just accept it.
For example, I've thought, what if I moved from my sorta 4- season climate to Deep South? I'd not need most of my sweaters, jackets. What if I retired in a year ? Many of the " work" clothes I've bought in past 2 years would not be needed. Yes, I would not HAVE to buy all new things, and less of a problem than fit, but I'd have the sense of loss of current wardrobe and need to buy some new things.
More to your point, I need to get back in better shape and if I am successful, it's likely I'd drop a size, and so if I'm still working, I'd need to replace some things. I did literally wonder if I'd like that and had to go, are you crazy?
So I'm reading more on minimalism, NOT because I need to be that, but as a reminder that if size/ fit changes, I really can get by with much smaller core wardrobe, so could still dress well, and in fact should do less " overbuying" for any one area of life. I am giving more though to the most useful key pieces, what I kind to repeat, and so on.
So all this is to say, go for it and trust that it won't change you overnight AND many items do fit over a weight/ size range. Also give some thought to running a tighter wardrobe of pieces that fit great and you'll have more budget for replacing since less is tied up in duplicates/ unworn items.