If they are still in good condition then they can at least be onsold to another navy. Further to that the ships will remain in service, I presume, until each replacement is accepted int service itself.River class Batch 1 is being withdrawn because we're buying Batch 2.
We're buying Batch 2 because we have a contract with BAE to spend a minimum amount on warships each year, meant to tie us into continuous build to avoid the waste inherent in stop-go.
Despite having that contract in place the MoD & politicians have failed to get their act together to order the planned ships, i.e. Type 26..
So we had to either give BAE the money for nothing, or order something.
Buying something has the advantages of keeping up workforce skills (one of the aims of the continuous build contract), & we can also get something better & newer than what we already have.
River Batch 2 was about the only thing that could start building quickly enough & would actually be useful.
So, we're not buying 'em because Batch 1 is thought to need replacing. It's the other way round.
It's a ghastly waste of money, entirely due to the shocking incompetence & indecisiveness of politicians, the MoD, & the RN high command.
The RAN has had decades of ships being withdrawn from service years before their replacements were ready - sometimes years before they were even ordered..
Still, that state of affairs in the UK is troubling to say the least.
MB