I don't think I buy the de-orbiting scenario... something the size of a space colony has a lot of momentum, and it would take a huge amount of energy (much more than even an impactor carries) to alter its orbit significantly.
The slow-leak scenario is a legitimate one, though I don't think it leads to slow death... it leads to increased resupply expenses. Even without micro impactors, you can't get any structure 100% airtight. The ISS, for example, loses about 230 g of air per day (reference). It's not a huge deal; you just top it off from the tanks. But obviously you'd prefer to keep that loss rate as low as possible.
(EDIT: And don't forget about self-healing materials... a real space colony will probably have a layer or two of these, which will automatically seal any small cracks or holes.)
The slow-leak scenario is a legitimate one, though I don't think it leads to slow death... it leads to increased resupply expenses. Even without micro impactors, you can't get any structure 100% airtight. The ISS, for example, loses about 230 g of air per day (reference). It's not a huge deal; you just top it off from the tanks. But obviously you'd prefer to keep that loss rate as low as possible.
(EDIT: And don't forget about self-healing materials... a real space colony will probably have a layer or two of these, which will automatically seal any small cracks or holes.)
Joe Strout
Lead Developer, High Frontier