The cutting back may affect the flowering, but shouldn't kill the plant - but how effectively you manage to move it is what makes the difference. After 8 years, the roots will be extensive and deep, and you may find you can't extract them sufficiently well, but it seems you have no choice but to give it a good try, so cut the top growth down to a few inches, then loosen the soil all round, trying not to break roots, extract as much as you can intact, and reposition in its new hole (which should be dug over already, and dig a much larger area than you think you're going to need - don't cramp up the roots to fit it into the new position, move extra soil away to accommodate them). Water thoroughly and frequently once moved and take heart from the fact that this rose is easy to acquire, and if it doesn't make the transition, you can always buy and plant another one.