Q. I have dedicated Linux server located in remote data center. My questions if sshd is restarts will any connections are disconnected?

A. No ssh will not disconnect your ssh existing ssh session. You can use normal ssh restart command:
# /etc/init.d/ssh restart

Similarly when you restart network ssh session will not be disconnected:
# /etc/init.d/network restart

However if you are making any changes to iptables based firewall script, you may loss the connectivity due to wrong iptables rules.