what will be the situation or story if there was no bertha mason(means unmarried Mr.Rochester)?

Every character supports different themes. If you take one out, the themes and continuity of the book is altered. Let's examine Bertha Mason. Bertha occasionally escapes from her prison and wreaks havoc in the house; her last outburst involves setting fire to Thornfield and leaping to her own death. As the representation of the classic Gothic figure of "The Madwoman in the Attic," Bertha is both pitiable and terrifying and supports Bronte's critique of gender inequalities and Victorian marriage during the period. Without Bertha, the context of Rochester's role in the book changes and hence, Jane has a different experience.