Would leaving like that put you in risk of being dropped into the Low Priority Queue? If so, while it would be rather considerate of you to do so for your team, I don't know that it would be advisable to do it too often.
If you're in a situation where you cannot leave and take the penalty, you can always consider trying to jungle without smite (which is admittedly rather difficult now) or playing as a duo top lane. It depends on the champion you are playing, as some champions are too weak in early levels to jungle without smite, but others can manage it with only minor difficulty. As far as duo top, start with one of the support items for gold income, and keep an eye on the top side objectives. It's less than ideal, but is still a perfectly winnable situation.