In my experience, unless you are already a big fish (ie someone that your SM knows by name and depends on your spending for the store) you do essentially start from zero when your SA leaves. In fact I think it’s even worse than zero because your new SA already has a full roster of clients to fight for and now you have to make yourself stand out against people she’s been working with already for years. It really sucks.
My SA left the company and this was essentially what the new SA told me when I met him It sucks but we fostered a great relationship from that point on.
(This was at a different US store)