You won't lose your number after 6 months of inactivity. It takes 12 or more. When you get back you'll just need to contact 48 support to get your account reactivated but your number will still be associated with your account. You might want to double check this with 48 support just to be sure but it's also covered in the terms and conditions.
Hope this helps.
I am not a 48 employee so if you need to contact 48 support then use option 3 or the chat facility here.