This sentence uses the correlative conjunction neither...nor... to connect two subjects.
The rule for subject-verb agreement with neither...nor... (and either...or...) is called the Proximity Rule.
The verb must agree with the subject that is closer to it.
In the sentence Neither the leader nor his followers \_\_\_ present, the verb comes after followers.
The subject followers is plural.
Therefore, the verb must also be plural.
is, was, and has are singular verbs. were is a plural verb.
The correct verb is were.