Ah, sorry now I've got what you want to know. 8時までにかえらなければなりません。 In this case, なければなりません。（なければならない）is rengo, idiom. We use this expression and we say so. https://www.weblio.jp/content/%E3%81%AA%E3%81%91%E3%82%8C%E3%81%B0%E3%81%AA%E3%82%89%E3%81%AA%E3%81%84 コロナがなければ、人に会える。 In this case, this is ない＋ければ→なければ, as you said, ない-form drops the い. They're different.

The verb's ない-form drops the い。 Yes, that's right. Therefore, ない＋ければ→なければ ない is thought to be adjective, in the Japanese grammar.

Let me explain this grammar from the beginning. E rhyming and ば means if. For example 行けば わかる means if you go you will understand. 行かなければ わからない means if you don't go you will not understand. コロナが なければ the verb we use here is ない which is the opposite of ある which means exist. But ない conjugate like i adjectives. コロナが なければ means if コロナ doesn't exist If you have more questions to ask me please request my lesson.

Let me explain this grammar from the beginning. E rhyming and ば means if. For example 行けば わかる means if you go you will understand. 行かなければ わからない means if you don't go you will not understand. コロナが なければ the verb we use here is ない which is a opposite of ある which means exist. But ない conjugate like i adjectives. コロナが なければ means if コロナ doesn't exist If you have more questions to ask me please request my lesson.