Whilst the British Library is spending a lot more money rebuilding, and expected to take a year or more to be fully operational again, there are some upsides to this. Their IT infrastructure used outdated and insecure practices, which enabled the attack in the first place, and the rebuilding forces them to modernise it. It also sidesteps the possibility of the ransomware group retaining a foothold in their systems, unbeknownst to the BL (though I will add that ransomware groups are, perhaps surprisingly, usually pretty honest once you pay them).