OK try this (no promises it will work - I have just brought up a working connection on my laptop this way but ymmv)
1. edit your /etc/network/interfaces file e.g.
gksudo leafpad /etc/network/interfaces
It will likely contain only a couple of lines defining the loopback interface('lo'); add the following lines
sudo nano /etc/network/interfaces
2. in case the broken network-manager is still running
iface wlan0 inet dhcp
3. (re)start the (alternative) networking service
sudo service network-manager stop
You may have trouble with (3) not restarting (I just did) - if so try rebooting instead
sudo service networking restart
This assumes you are getting everything via DHCP - if you need to set up non-DHCP supplied DNS servers or a wholly static IP we will need to add more lines.
Once it's up you can confirm whether you have a working connection and which service is configuring it e.g.
service networking status
service network-manager status