if i was to beleive in the statement of the answerer then where would i place the whole life of prophet (saw) which as per quran is the uswa’a for all. Now if i read this hadith and relate it to the uswa’a hasanah that i get the rightful meaning of the hadith! Yes the hadith informs that khilafah shall be established and from the sunnah its clear that if its not then its obligatory for a muslim to work towards it. Whether it happens in ones lifetime or not is not important but what is of prime importance is to follow the manhaj fm the life of Prophet(saw). And by doing this one cannot but be working on the path to establish khilafah.
While we need to recognise and appreciate all sources of understanding Islam and the life of the Prophet (pbuh), it is important to distinguish between the sources through which we should get our obligatory beliefs and practises and those that at the top of that gives us other helpful information in order to be more successful in our path of life as a religious person.
The sources of understanding Islam are the Qur’an and the Sunnah (there is a great deal of material on the definition of Sunnah on this website that you may like to read).
Hadith is a great sources for understanding the history of Islam and the life of the Prophet (pbuh) as a role model. Hadith also facilitates the understanding of the Qur’an and Sunnah (although it is not essential for that purpose).
If you believe that Hadith is in fact the source of understanding Islam then I would like you to explain for me that in what sense the path of guidance is clearly explained to us (as stated in the Qur’an) if parts of it was supposed to reach us in the unreliable way that Hadith has reached us (that is through a few fallible individuals in every generation – at best – who often transmitted not very relaible and not very consistent or thorough information and not necessarily the exact words of the Prophet – pbuh)?
However, if you agree with us that Hadith is not the primary source of understanding Islam but is in fact a very valuable though a secondary source, then you will look at Hadith in the light of the primary sources that are the Qur’an and the Sunnah. If you do that then your understanding of a reliable Hadith will be inline with the understanding that you will have from the Qur’an and the Sunnah.
To come to the specific issue of Khilafa, as it has been explained in a number of answers on this website, while it might in fact be a very good idea to unite all Muslims under one system of Khilafa, there is no definite instruction in the sources of Islam (including the primary sources and the secondary ones when looked at under the light of the primary ones) to make it obligatory for Muslims to establish Khilafa.
Having said the above, if you, as an individual, have understood a Hadith to instruct you as a Muslim to establish Khilafa and if you consider that Hadith to be reliable (i.e. definitely the words of the Prophet – pbuh), then it will be your religious duty to follow your understanding. Obviously you cannot expect others to have the same understanding as you.