IMHO, if you must move from TSM to Veritas NetBackup, (typically a bureaucratic or economic reason, not technically based) just start using NetBackup and stop using TSM. Then keep TSM running on a 'warm' server, and test restores and migtating from tape to tape occasionally. You can pretty much get rid of the disk pools, but you will need to keep TSM 'alive' and ready to restore until you are ready to call it 'dead' for your use.
I hope you never have to do this. But this is how we migrated from Veritas BackupEXEC to TSM, and given our 60 day retention window, it was acceptable. This is also how a IBM VAR is suggestion we migrate to a new TSM server (from Windows to AIX), but that seems odd to me. ... Jack