The Quran is very clear about this Surah Imran:55
اِذۡ قَالَ اللّٰهُ يٰعِيۡسٰۤى اِنِّىۡ مُتَوَفِّيۡكَ وَرَافِعُكَ اِلَىَّ وَمُطَهِّرُكَ مِنَ الَّذِيۡنَ كَفَرُوۡا وَجَاعِلُ الَّذِيۡنَ اتَّبَعُوۡكَ فَوۡقَ الَّذِيۡنَ كَفَرُوۡۤا اِلٰى يَوۡمِ الۡقِيٰمَةِ ۚ ثُمَّ اِلَىَّ مَرۡجِعُكُمۡ فَاَحۡكُمُ بَيۡنَكُمۡ فِيۡمَا كُنۡتُمۡ فِيۡهِ تَخۡتَلِفُوۡنَ
The word used is mutawaf'fika. means give you death. Even in urdu we use the word, wafat meaning death, Dost ke walid aaj wafat paa gaye just to put it into context. No where in the Quran it says he was raised up alive. Unfortunately almost everywhere this has been mistranslated to fit into the raised up alive narrative.
And then again in Surah Maida 115-116 Allah asks Prophet Isa a.s did you ask your people to worship you and your mother Mariyum a.s besides Allah. And Prophet Isa a.s will say no I only did what you asked me to and I am free from any blame as to what they associate to me and my mother and until I was among them I always guided them to true Tawheed.
But if he was to comeback shouldn't he say. I have just come back and put all of them on the sirat ul mustaqeem.
Also nothing about the Mahdi in the Quran, if such a huge event was to take place that another prophet is to return and then a "mahdi" and all the following presumed events to take place, don't you think it would be mentioned. It's not even mentioned in passing.
As much as I remember there is nothing about the coming of the Mahdi even Bhukhari or any other authentic hadith anywhere else. Just some vague narrations from lesser books.
So as far as I am concerned, Prophet Isa a.s is not coming back ( if anyone was to comeback, shouldn't it be the most superior and loved Prophet, that is Prophet Muhammad s.a.w ? ) And there is no such thing as the mahdi.
This was just a Christian concept adapted or maybe inserted as a morale booster because the people were tired of the oppression of the ummayid caliphate and its tyrant kings. Thats why you will narrations of a mahdi appearing in Sham on a shiny white minaret. To give hope that one day someone will come and rid them of this tyranny.
Just the same todays muslims basically just chill and just things be, waiting for a mahdi to come and conquer the world for them over which they will rule till the end of time. So why waste any effort in bettering yourself or trying to catch up with the rest of the world. Just leave it to mahdi.