I'm a graphic designer (check my bio).
Graphic design is not an easy industry to get into, i studied for 6 years before getting my first job. I did alot of design work in my free time as well, to hone my skills. I would recommend taking a college course at HNC level (UK) which could lead onto receiving your diploma, as a start. (Diploma is optional, not all companies offer Grad jobs straight after university.) Another way is by applying for internships and placements, sometimes these may have to be voluntary. I tried for around 8 month before being afford a 3 month voluntary (un-paid) placement, but i took it. I worked my socks off and was offered a job at the end as an engineering designer. Also make sure you have a large skill base, such as AutoCad, Photoshop, Illustrator, In-Design and Flash - These are all huge elements of Graphic Design, you will pick up smaller aspects and software along the way, focus on the ones i have mentioned.
Now i have been through that i can answer you:
1.) Graphic Design pays depending on any other job, How good you are and how consistent your work is. My example i am going to use though, is working for a firm, not free-lance.
A starting pay salary for a Junior Graphic Designer will range from about 14 - 19,000 pound (UK). If you already have alot of experience behind you and a stepping straight into a design job, not as the junior, you can expect a salary of anywhere from around 22 - 32,000.
Now, moving onto experience and time. Once you have acquired the skills to become a Senior Designer, you can earn anywhere from the amounts of 50k +.
Combine this with freelance work out of office, from home and you can easily earn anywhere in the triple figure mark.
2.) Graphic Design will not eventually die out, infact i have been told that there will be a HUGE opening of jobs in the design industry within the next 5 years. Photography is extremely hard to get into, along with multi-media, and unless you are extremely talented you will not be making as much money. Remember you need to be passionate.
With whatever you choose, i hope you do well.
Just to give you a basic idea, i'm a Junior CAD Designer, i have worked here for a year, i'm 22 years old and earn just over 24k a year. (Before tax) Per annum.