Whats better? catch old urls or wait till im indexed again?

[john1000]

Hi,

Sorry but i couldnt find a proper title for this..
I could use some professional opinion if possible..

i decided to kick out my old forum cause it was unreliable.
i installed a new forum , simplemachines.

thing is, i do have my old forum topics in google and i was wondering..
what would be better..
Trying to catch my old urls by some script or rewrite so people get redirected to my new forum, or make sure every old forum url hits a 301 or whatever needed to let google know it doesnt exist anymore..?

[ZydoSEO]

Always 301 redirect old pages to equivalent new pages and wait for all the links to your old forums to be recrawled.

[john1000]

I see, i can understand that..
But with the system i use im using some sort of plugin that turns the old urls to the new one but no 301 is involved.
But as the old ones dont exist anymore,wouldnt they just disappear?