You asked two questions... the first was:What happens if I do not reply to the annulment within the 30 days which was served to me?
The Court will grant a default judgment. It might be a divorce, or it might be an annulment. It really depends on the Judge, but it really should be a divorce, even though he asked for an annulment. An annulment based on fraud must go to the basis of the marriage, such as you claiming to want many children just like he wants, then he finds out you had a hysterectomy. Or wanting a traditional Catholic family, you claim to be Catholic, then he finds out you are a very different religion. They are not easy to obtain, but I have seen it done.
The second and third questions are:If I reply back saying a request for separation due to irreconcilable differences, what happens then for both the petitioner (my spouse) and the petitioner (me)?
You two will go through the divorce process, which includes the actual divorce, child and spousal support
, and custody/visitation issues.
What are my available options to extend the marriage as long as possible now that an annulment has been served on me?
I don't know what you mean by "extend the marriage." If you mean reconciling, that will be up to him. If you mean for property purposes, most property issues, such as retirement, will use the Date of Separation as the effective date to end the marital interest in the property.