Bonsai.

I was entrusted with looking after my son's girlfriend's bonsai when they went on holiday. Told to water it every couple of days. Did so at first, but then forgot for a while when I was worried about my dog. Also put it behind some curtains [it was quite warm at the time]. The weather turned and I put the heating on..radiator was next to the curtains. I didn't miss all that many days but it is now shedding it's leaves quite dramatically..do bonsais do that?? No one should ever entrust me with a pot plant as I am the kiss of death. Any bonsai experts out there? Wondering if they'd notice if I replaced it with a similar one and worried that it was a special gift from someone. I had one like it myself years ago [and that died as well]. Oh dear .