There are two independent clauses in the sentence,

1. Plans change

2. People must adapt

Plans: this is the subject of the sentence.

Change: It’s the predicate, action that the subject performs.

Taken together, ” Plans change” is an independent clause since it has both a subject and predicate and expresses a complete thought.

“People must adapt” is also an independent clause as it also has both subject and predicate along with the adverb “must”.

The sentence, however, is not grammatically correct in that the coordinating conjunction “and” must be preceded by a comma to have the correct punctuation.

The rectified sentence is:

Plans change, and people must adapt.

I’m glad to have been able to answer your question.

But needs a few words to be more wholesome

Verb: Change

Subject: People

Verb: Adapt

Yes. Every subject has a verb to back it up