I don't think if leverkusen will lose 4 straight matches, considering their 9 up coming matches I think Frankfurt, dortmund, freiburg, stuttgart,this above mentioned club is considered been a threat to leverkusen. but I'm pretty sure that if leverkusen is going to lose I think it will only be 2of their matches, which is either to dortmund or freiburg,I don't consider the rest as threat to leverkusen instead of this teams to win leverkusen they will make it draw.
I no longer even consider all of these teams to be a threat to Leverkusen because Leverkusen's biggest threat this season is Bayern Munich and that team has also been defeated by Leverkusen this season. So I no longer consider all the teams you mentioned to be a serious threat to Leverkusen so it could be quite possible for Leverkusen to continue this unbeaten streak until the end of the season even though it is also possible for Leverkusen to get a draw in the remaining nine matches.
Well maybe the big teams aren't a threat but football sometimes can be really funny and maybe you can be surprised that it might even be one of the little teams that even give them problems in their quest to keep a clear stand and achieve something that very hard to do which is keeping an unbeaten record through out the whole league. Bayern Leverkusen have really shocked many this season and they have defiled all odds and is heading to win the bundesLiga but you can never be too certain because one bad spell can spoil everything.