MaybeNeverTransformer.swift

import RxSwift

struct MaybeNever<S: AnyObject> {
    private weak var take: S?
    init(_ t: S) {
        take = t
    }
    func run<A, B, R>(_ f: @escaping (S, A, B) -> Observable<R>) -> (A, B) -> Observable<R> {
        return { a, b in
            if let t = self.take {
                return f(t, a, b)
            }
            return .never()
        }
    }
}

someValues.flatMapLatest(MaybeNever(self).run { $0.sendRequest(value1: $1, value2: $2) })...