Will specifying 'LOSTERM=IMMED' prevent sessions from hanging in a Network failure scenario?
If a VTAM NSEXIT is not used, then a 'hang' in a 'PNFYxxxx' state may occur because it is not possible to run a CLSDST after a lost Terminal event has happened. So to avoid the PNFYxxxx state, adding the parameter 'LOSTERM=IMMED' to the APPL statement for an individual Node or Group would be very likely to resolve this Issue, eg.:
node0001 APPL EAS=1,MODETAB=modetab,DLOGMOD=M4NSNA,LOSTERM=IMMED
When 'LOSTERM=IMMED' is specified and no NSEXIT Routine exists, an 'INACT' or 'TERM' will cause VTAM to call the LOSTERM exit with Reason Code of 48 (x'30') and the session will be ended.
So, in conclusion, "yes", coding 'LOSTERM=IMMED' is very likely to prevent this problem.