If email delivery fails to one user, does it fail to deliver to all users?

I see an email back saying delivery failed from the recipient's ISP. Is it safe to assume that the other recipients still got the email? Or is there some kind of signaling back to my ISP preventing delivery to any recipients and thus canceling the email.

No, when you send an email it is sent to all of the recipients individually.

You should get a "delivery failed" for all of the recipients that failed to get the email for whatever reason. If you do not get a delivery failed notification then you should be able to assume that the email got through.

Depending on the email systems in question though it may be a couple of days before you get the notification as servers may try to resend the email and thus delay the "failed" response.

No, if you have sent let us say to 10 E-Mail addresses, and you get a mail from the Mail Delivery Subsystem saying "Address not found", then the mail is not sent to the mentioned address(es) alone, for others it will be delivered.

I tested this out with couple of my own email ids.