// ... if Labour do manage to form the next government would they really change the system that put them there? //
Possibly not, but it's happened multiple times before. Think of the many times that the vote has been extended -- most notably the 1832 and 1867 Reform Acts, the 1918 Act giving the vote to women (over 30), and the 1928 Act extending the vote to all adults.
What's particularly interesting about these Acts is that, after the 1867 and 1928 Acts, the Governments who introduced them lost the subsequent elections. The 1918 Act is more complicated to assess, because of the Lib/Con Coalition staying in power but swinging sharply Tory. So sometimes reforming does backfire, but we can surely be grateful that the Governments in those cases were not cowards, as both times the reforms were essential.
A more likely scenario here would be that the reforms implemented are smaller in scope than are being called for here. Most notably, I don't believe that Lords Abolition is likely any time soon, although hopefully measures will be taken to drastically reduce its size and the manner in which new Lords are appointed (eg severely limiting the number of political appointments, removing all the remaining Lords Spiritual, etc.), as a step towards reform or replacement with an elected (or semi-elected) second chamber.