Every Publisher Pitch carries an acceptance deadline, shown on the pitch itself.
Once the deadline passes
The pitch expires. It can no longer be accepted, countered or actioned, because the editorial opportunity behind it is usually tied to a publishing date, a seasonal moment or a slot in the publisher's calendar.
The deadline is set by the publisher and can't be changed or countered. A counter-offer in progress doesn't extend it, so an active negotiation will still expire if the date passes.
If you still want the opportunity
An expired pitch can't be revived. If the publisher and the idea are still of interest, set up a campaign and pitch them directly — see What do I need to set up a campaign?
Avoiding missed pitches
Keep Publisher Pitch Activity notifications switched on, so you get the pitch and its reminders
Check Awaiting Acceptance regularly — it shows everything currently waiting on you
Make sure the right people at your company are set up to receive pitches