1957 Seamaster - Sliding Clasp Beads of Rice

Sad to read you've already sent it to Omega.

Typically they charge a lot of money and replace a lot of parts is all, they try to make the watch look new but that can mean it won't be the same afterwards, most collectors tend to replace crystals and seals but try to preserve dial, hands, crown, and not polish the case, independents will do that and allow the owner to maintain a higher degree of control over the result for a lot less money than a restoration.

As for the bracelet links, I have one of those sliding clasp bracelets and it uses the same early style beads of rice links as the normal snap-clasp style version, so you should be able to buy some loose links pretty easily off eBay, or the parts section here, just keep in mind there are many fakes.

You don’t need to send to Omega better choice is Omega certified independent watchmaker with Omega parts account.
Omega is much more expensive and they will replace whatever parts they like and will reduce vintage appeal and value of original watch.
Can you get it back from them as once they start you have no control regarding what they might do.

Edit: @dsio faster !