Moulana Qasim Nanotvi says " A Prophet can even come after Muhammad (sallal laahu alaihi wasallam).If such a prophet comes khatam ul nabuat won't be effected
Translation
" If we assume that in future there comes any other prophet, this will not make any change in the finality of prophet ( khatmiyat muhammedi)"
("Tahzeerun Naas")