my eldest was 8 months old when he did something similar, just crying in the cot even though I was sitting next to him on the floor. I got fed up and left, he was beside himself and cried (snotty choking shrieking) and cried and got into such a state he was sick.
next night the same thing was repeated at which point I thought that leaving him to cry it out until he vomits was insane, in his case anyway.
I don't generally leave my kids to cry until they fall asleep, but has done it on occasion.
I don't like to ignore them and if they cry out having been asleep I always check what happened - we've had stuck elbows & knees between the cot bars, sickness in the night, naked children who took their clothes off when briefly waking up then managed to pee all over the cot only to wake up again shivering in their own pee and many more....
at 7 months I would do whatever keeps them quiet and happy - probably not "correct parenting", but I'd rather cuddle them to sleep then clean up vomit and feel incredibly guilty!
btw my eldest is almost 12 and still has trouble falling asleep, he just doesn't seem to need that much sleep.
baby's 1 and I've just BF so she's either up 3 times looking for the breast or sleeps through (9pm-7am), hit or miss really.
the others are fairly good sleepers, usually asleep between 8pm - 9.30pm (ages 3, 6, 8 & 9) - up at 7am-7.30am
they all sleep through the night usually, so maybe making them feel safe is better than "doing the right thing"?
I have tried Tracy Hogg's shush/pat method with some of them, the results varied, mainly positive, so it is a good technic IMO.
hope this helps