Once SDL contract is over, what happens to the current running site in
production? Will that stop working?
Yes (if the question tags are correct). But, even if it continues running, having it that way would be using unlicensed software which has legal implications. Contact SDL (RWS) directly to see what your options are.
See also Nuno's comment below. ...
There are 2 reasons for that:
slow VPN tunnel (full tunneling is more than 5x times worse), sometimes 100x slower!
cache issues (or disabled at all)
We have fixed many cache errors in latest DXA app and UDP stack