One of Rigby Road's more outlandish advertising schemes, must have cost Walls a fortune! A number of Balloons have been retained by Blackpool Transport and, as cainebj says, converted to 'fit' the new network. Many others have been sold off to private owners for preservation - some with brighter futures than others.
Just come across some pics of 719 in it's current guise, showing the (awful) current standard livery. I've not been on the tram recently, but there is one clue to it's previous Walls identity, and that is the horizontal 'slats' moulded into the lower front panels, just above the black 'bumper' strip. These were part of the quite elaborate exterior modifications carried out when the tram 'went Walls', and presumably it isn't worth the bother of taking them off.
http://www.flickr.com/photos/dalrigh/8148744595/
Incidentally, however dodgy 719 might look in this state, it isn't remotely as bad as 700, which went from being a perfectly preserved heritage car to looking absolutely hideous, with a terrible mish-mash of original 1930s features melded in with automatic doors and the nasty livery. Absolute sacrilege.