How will the search results of Yandex and Google react to the radical redesign of the site?

Question

Search Engine Optimization

The theme is children's camp.
There is a site dedicated to the very first shift (age 8 months), somehow indexed by search engines. I placed landing pages for other shifts on subdomains.
I want to replace the first shift site on the main domain with a general camp site with links to shift subdomains.
How will the search engines react to this?
Will positions drop?
That is, I plan a radical redesign and expansion of the subject.
Are there any pitfalls?
Logically, I think at least to keep the "site map" - that is, to leave all the pages as they were called before.

Answer 1

If the structure is not changed, only a slight temporary decline is possible.