I'm sorry to hear of your loss. Unfortunately, an empty sac can occur with a partner who doesn't have sperm issues. I actually found out we had an empty sac embryo when we did genetic testing on our embryos. Chances are that your next pregnancy will be just fine. Wishing you the best!!
Lower motility and lower count don't necessarily mean there aren't healthy sperm there - just that there are fewer. There is always the possibility of physical or mental disabilities with all pregnancies, but the vast majority of pregnancies result in genetically healthy babies. I'm sorry for your prior loss. I had several and know how stressful it can be to be pregnant again. I hope everything goes smoothly for you and you bring home a healthy, happy baby in just under 9 months!