It's not essential to get a 2:1 to secure a job at a top law firm, let alone a law firm. It's important to realise that it'll, obviously, make securing a job at a top firm that much harder to obtain, but it doesn't necessarily spell the end for your career as a solicitor.
First off, in relation to gaining a 2:2: you'll certainly be able to obtain something, providing you have experience and extra curricular activities to support your CV. Obviously, firms look for these as standard, but the more relevant experience/extracurricular experience you have, the better. I have yet to do a vacation scheme, but intend to do one in third year (providing I achieve a better 2:2/2:1 and spend more time on the applications), however, in the mean time I'm working at several firms and a chambers in Sydney this summer. Any extracurricular or legal experience you can gain will help: vacation schemes, working a few days a week in a solicitor's, mooting, volunteering at CAB etc
There's plenty to do with a degree, even if it's working in a regional solicitor's. If you want to go into the profession, it's worth a try, despite the cost of the LPC. If you don't want to teach, don't teach. There's plenty to do other than teach with a law degree; such as going into finance, doing something else after the degree (i.e journalism) etc are all popular alternatives.