Rescheduling Zoom webinar without a new date

We need some advice on a situation in which we find ourselves.  

We have a Webinar set with a speaker tomorrow (Nov. 3rd) and currently have 140+ registrants.   He is a trial attorney and contacted us late yesterday saying he's been called to trial and is unavailable.  He does NOT know when he'll be available yet.  

Questions are:  

  How long is the webinar link good for if I have to set a tentative date?  Can I set it for sometime in Dec. or does it need to be within the next 30 days?  

  If I set a tentative date (say 2 weeks in the future), can I change that date again to another 2 or 3 weeks in the future while retaining the webinar link?  

  I understand the registrants will get an email when I change something in the webinar, so I'm not concerned about that.  My main concern is how long the webinar link that they currently have is retained and usable.  

 If I can keep kicking the can down the road while our presenter gets a new date, we'll be alright.  But if I have to create a new webinar with a new link and then get people to re-register, it could be a super-cluster. 

Many thanks!