As far as I understood so far Subscriptions are independent of ClientSession like described here "7.11 Subscription Service Set" https://reference.opcfoundation.org/v104/Core/docs/Part1/7.11/ ) or at "CloseSession" parameter "deleteSubscriptions" ( https://reference.opcfoundation.org/v104/Core/docs/Part4/5.6.4/ );

Therefore also corresponding parameters at "CreateSubscription" ( https://reference.opcfoundation.org/v104/Core/docs/Part4/5.13.2/ ) exist like e.g. "revisedLifetimeCount":
"...
revisedLifetimeCount Counter The lifetime of the Subscription shall be a minimum of three times the keep-alive interval negotiated by the Server.
..."
Unfortuneatly those parameters are mostly "counters" (and not time values / time intervals), but I could NOT find a concrete time / time interval mentioned e.g. by "keep-alive interval negotiated by the Server" or other occurences of "keep-alive time interval". I would assume that e.g. TCP keep-alive is not what is meant here, or?

I have only come across "KeepAliveTime" at "6.2.5 WriterGroup Parameters" ( https://reference.opcfoundation.org/v104/Core/docs/Part14/6.2.5/#6.2.5.3 )
"...
6.2.5.3 KeepAliveTime
The KeepAliveTime with DataType Duration defines the time in milliseconds until the Publisher sends a keep alive DataSetMessage in the case where no DataSetMessage was sent in this period by a DataSetWriter. The minimum value shall equal the PublishingInterval.
..."