I would have thought Lallana would just ignore tweets from insignificant idiots. Let's face it - he has ignored all mine!
That aside (and sorry - I haven't read the entire thread) I would have thought it would take more than a few abusive tweets to make him close the account. Footballers (indeed, anyone using twitter) surely uses the service in the full knowledge that this sort of thing would happen all the time. Look at the sh!t Billy Sharp got.