* Can one teacher replace another teacher in a classroom setting? Yes, absolutely. Substitute teachers regularly replace absent teachers. Long-term replacements might occur due to leave, illness, or resignation.
* Can a teacher be replaced by a different teaching method or technology? Partially. Technology can assist teaching, but it's unlikely to fully replace a human teacher, at least not in the foreseeable future. Different teaching methodologies may be more or less effective depending on the context, but again, a complete replacement is doubtful.
* Can a teacher be replaced by a parent or guardian? No, in a formal educational setting. Parents can homeschool their children, which is a form of education, but it's not a replacement for a certified teacher within a school system. Parents may help with their child's learning, but they are not qualified to take the place of a teacher in school.
To get a clearer answer, you need to clarify what kind of "replacement" you're asking about.