setting aside exparte decree

Are you saying that "perpetual injunction" was the claim and whole claim and that's the only precise reason for which plaintiff approached court?

And under what basis/circumstances or 'facts in issue', such a kind of claim arises? (or rather has arisen vide plaint?) ........................  Very Interesting!!

Yes. The defendents may apply under Order 9.

Clarification :-

I am not at all saying it wrong or erroneous, finality of judgment may also cause a temporary injuction converted into perpetual injuction.

Set aside of Ex-parte looks at only following and not onmerits of main case ......

1) service of summons/any element of fraud and

2) cogent reasons for failure/delay and extent of delay in responding to it and

3) whether allowing of set-aside would deem infructuous due to after events/circumstances post decree and time delay.