Unless something changes, disaster will surely ensue .

The crowd was further agitated by the police, causing a riot to ensue.

"Ensue" is not a noun; it is a verb. Only nouns and pronouns have plurals in English.

A noun meaning "that which ensued" would be "result" or "consequence".

However, "ensue" is the form of the verb used with plural subjects, as well as "I" and "you".

ensue

After the car swerved in front of the truck, a chaotic accident ensued on the highway.