Urgent advice on exparte

They can file application to call back exparty orders, generally court allow that after imposing cost on applicant.

Yes, Opposite Party can re-enter the case by filling an application under Rule no.13 of Order IX in the Code of Civil Procedure, 1908 to set-aside the Ex-parte Decree given in your favour.

However, the Court will not simply set aside the ex-parte decree given in your favour 'without' issuing you a notice informing you that such an application has been filed against the decree granted in your favour.
Court will issue you a notice under Rule no. 14 of Order IX of the Code of Civil Procedure, 1908 to show-cause as to why ex-parte decree should not be set aside.
Then, you have to contest in order to protect the decree/order given in your favour. After hearing both sides the Court will decide whether the Ex-parte decree should be set-aside or not.
If your ex-parte decree/order remains unchallenged for 3 months from the date of Decree, then your case will attain finality meaning the opportunity for opposite party to appeal against the Ex-parte decree/order will be barred by Limitation.

However, even after 3 months the Opposite Party can appeal against the Ex-parte decree provided the delay in filling the appeal has been condoned by the Court under Section 5 of the Limitation Act, 1963.
Delay can be condoned by Courts on medical grounds, death in a family, absence due to particiaption in some family functions due to which the Opposite Party was unable to contest the Lawsuit.
Furthermore, in property cases people don't give up fights (read : Court Battle) easily. In fact, anything which involves money, assets, wealth & property; people fight or contest till the highest Judicial Forum (i.e.) Supreme Court of India.

Good Luck.
All the Best.