Yeah you can get by. It affects you. Most teams can get by with a hobbled rb. The pats run d has been suspect but high tower was back and it helped. Obviously it would've been different, but if cannon, lewis, and to a lesser extent edelman(marshalls dropped td was bad, edelmans was arguably worse, his finger has been an issue the past 2 weeks) were healthy it wouldn't have been very close.
I'd argue that having some 3rd stringer at LT who can get help in varying ways, has less of an effect on the offense of the Patriots than having a busted Ivory in the backfield. Patriots can go on with their game plan without much of a hitch because they can adjust protections, Brady has a safety valve in screens/dumpoffs etc, not to mention he can spam those short crossing routes which take minimal time to throw. Which also seems to release some of the pressure from the passrush.
The Jets have to rely on the production of Ivory because it is complementary for how their team in comprised. Ivory has been the engine of the offense, and helps rest their D and kill clock to protect any lead or keep the opposing offense off the field. I think you underestimate how important he is to them, and how productive he's been prior to being gimped up in this game.
On the average, yes an LT is more important than an RB, but considering what we know of both teams, Pats make up for it more easily than the Jets can in this instance.