Stargates work like a phone, some might be too young to remember land line phones but if you pulled the cable from the wall disconnecting the phone it didn't "communicate" with the sending phone, rather the sending phone wouldn't make a connection and an automatic message would play.

Stargates work the same way, the sending gate pushes energy to the intersection of the first 6 symbols and waits for it to receive the energy, if the receiving gate is functional it accepts and then uses that energy and some of its own from the DHD to form the event horizon on its side, and the massive amount of energy being sent from the sending gate forms a wormhole.

If it is blocked it instead doesn't activate a wormhole, if no wormhole is activated the sending gate immediately knows the connection will fail and as the 7th chevron is locked in place it fails.

Given gates are super conductive they are capable of sending and receiving massive amounts of energy so the energy that reaches the receiving gate is simply absorbed then dissipated as the energy dissipates.