Windows wallets are available. You can also compile from source, if you are so inclined.
The update provides a interim fix to a bug in the Masternode payment code, which will activate after block 649620, which is less than 24 hours away. A rogue miner is running custom code to exploit the fact that MN payments can go down to zero as a result of the rebalancing process. You are asked to update as soon as possible to avoid being on the wrong chain, as this release may result in a fork.
If your node fails to sync on update or after block 649620, and your log file has rejected block error messages, you will need to clear your STRAKS state directory (e.g. .straks dir on linux), retaining your config files and wallet.dat files. Upon restarting, your node should sync as expected (but may take time).