To avoid misunderstandings, note that a single server instance can be configured to use multiple adapters, hence there is a 1:1 relationship between Server instances and Remote Adapter instances only if the Server is configured with only 1 Proxy Adapter.
If you run one Server instance and multiple identical Remote Adapter instances, only one adapter will connect successfully.
Then, if the adapter fails and the Server is configured to use a "robust" Proxy Adapter, a new adapter instance will be able to connect.

During the replacement phase, the client session is not closed, but will experience problems.
If you refer to a Metadata Adapter, subscription requests and client messages will be refused.
If you refer to a Data Adapter, no updates will be received.
Moreover, the adapter replacement is not seamless, unless you ensure that the new adapter instance shares the state with the previous one. This is not handled by Lightstreamer.

The way the new adapter can reconnect depends on the configuration of the communication between the Server (i.e. Proxy Adapter) and the Remote adapter.
If the Remote Adapter connects to the Proxy Adapter, then multiple Remote Adapters can compete for the connection and only one will succeed at any time.
If the Proxy Adapter connects to the Remote Adapter (since Server version 7.4), then you can place a Load Balancer in between and have all the Remote Adapters listening and only one at a time will receive the connection.