PM.Connect and PM.IsConnected are related to the PersistenceManager's connection to the PersistenceServer, so won't tell you anything about database connectivity. If you're not using a BOS the PM is always considered "connected".
To check whether you can connect to the database you can use PM.CheckDataSourceKey(keyname), or if you already have the RdbKey, key.CheckConnection(). Both methods do the same thing, and will try to open a connection to the database.
DevForce creates a new connection for every query or save, so there's no way to "reconnect" per se. If the datasource cannot be reached the above methods will return "false", but there's no automatic retry or reconnect logic.
If you suspect the network connection has been lost, you can also use the NetworkChange and NetworkInterface classes in .NET to help monitor connectivity.