Well, they wouldn't have been actively destroyed. Perhaps the only lasting scholarly consensus over 476 and the end of the Empire is that nobody wanted the Roman Empire to be destroyed. The Germanic leaders, like Odoacer, Theodoric, Alaric, even Atilla to an extent were all fighting for a place, or a larger place, within the Imperial system rather than to destroy or take from the system.

But the infrastructure did go away (largely--there were places in Spain and North Africa using Roman aqueducts into the early twentieth century, in fact, the Proserpina Dam in Spain is still in use) and that needs to be explained, but it is best explained through neglect. As durable as the aqueducts were, they still need maintenance even if the structure itself remains sound because the pipe might need replacing or be cleared of calcium accretions. This can be seen historically, as during the Augustan period a Senatorial office for water management was created, and we have several examples of donation made by private individuals to keep aqueducts in good repair (such as at Aspendos in Turkey). So infrastructure would fall into disrepair because the decline in urban life at the end of the Empire in the West meant that nobody was taking care of it.

For mines, it depends on the time and place. The massive Spanish mining operations, for example, were largely ended at the end of the second and third century, probably due to the chaos that engulfed the Empire at that time. The large mines at Dolaucothi in Britain continued into the fourth century, and may have been abandoned simply because they weren't profitable anymore, but smaller operations continued for some time after. As /u/idjet describes in the other post, mining continued in areas through the Early Medieval period, although on a smaller scale.