System Compatibility with the Old Client?

I've just discovered that Microsoft have introduced a new version of what was
a relatively stable system. We've used it for years successfully - as Im
sure tens of thousands of other people / businesses have globally.

Can someone just confirm to me if the old client will still work when
Microsoft finally bring up the network again - or will we be forced to use a
client and new functionality that seems to be very unstable to say the least.

We only used the functionality to sync several computers - can anybody
recommend a reliable replacement servic - as I think the writing is on the
wall here.

Thanks