I had the problem of invisible mouse pointer after an upgrade from Ubuntu 14.04 to 16.04, though the mouse pointer was always invisible (even after several reboots). Plus neither the solution to press 'Ctrl + Alt + F1' and 'Ctrl + Alt + F7' successively, nor to enter commands in the terminal worked for me.
But I tried the solution of user417467 edited by Ravan, which you can see here Mouse cursor invisible after 15.04 update. So here is what I did :
Open a terminal ('Ctrl + Alt + T' for me) ;
sudo apt-get install gdm to install gdm ;
In my case, the installation ended by the question wheter I wanted to use 'gdm3' or 'lightgdm' as display manager. I chose 'lightgdm'.
My mouse cursor was back, and everything seems to work fine so far.