Unable to return omamori

I have a question in regards to the return of omamori to shrines / temples after a year.

My Japanese penpal had expressed his wish to purchase an omamori for me, which I will receive when he visits me in October.

My concern is that I will not be able to return the omamori to a shrine the following year. Is it considered bad luck to keep an omamori forever?

Personally, I think it looks beautiful and will like to keep it as a souvenir. However, I am not sure if I will like to keep it if it is meant to bring bad luck.

I am also worried that I will offend my penpal if I reject his offer to buy an omamori for me.

Thanks in advance.

Hello!(^-^)/
Don't worry, you can keep it as long as you like and return whenever it's convenient for you.
No strict manner to omamori, to tell the truth, manner to return old omamori every year is a way to increase prayers of the temple/shrine.
If you neglect omamori, it bring bad luck, maybe?

See also:
http://www.japan-guide.com/forum/quereadisplay.html?0+104476

You can keep the Omamori forever. It doesn't mean that the momamori brings bad luck.

Thank you so much for your replies. Appreciate it. :)