I am not a part of the 'Accountants Union' but oftentimes when deadlines are missed the taxpayer is often at fault with information brought in late or incomplete. Just make sure that you are not leaving a good accountant and taking on a bad one. Your accountant should be 1) qualified with a practicing certificate 2) be able to talk to you and explain your affairs clearly 3) be confident enough to not be afraid of you 4) must not be so reliant on your fees that he cannot give you strong advice 5) be pro-active with your affairs.
If the accountant is at fault, bar the death or illness of a near family member, there is no excuse and you should leave him/her.
If your company's most recent CRO annual return date deadline was missed, you will need to have a registered auditor to audit your next set of accounts.
Presumably yes, but unfortunately the audit regulations are so difficult nowadays that most firms aren't exactly fighting for new audit clients (particularly once off's)