If one leaves his house to daven Ma'ariv before he Bentched (Birkas Hamazon) and then comes back home , may he Bentch then
Not only may he bentch, according to many Rishonim he has to bentch before he can continue eating (as opposed to the opinion of the other Rishonim, that he may continue eating when he returns without bentching first, and bentch when he is done).
Rambam Hilchos Berachos 4:3:
היה אוכל בבית זה ופסק סעודתו והלך לבית אחר. או שהיה אוכל וקראהו חבירו לדבר עמו ויצא לו לפתח ביתו וחזר הואיל ושינה מקומו צריך לברך למפרע על מה שאכל וחוזר ומברך בתחלה המוציא ואחר כך יגמור סעודתו
If someone was eating in one house, and stopped to go to another, or he was eating and his friend called him out to talk to him, and he left the entrance of his house and then returned, since he changed his location he needs to make a beracha on what he ate, and makes a new hamotzi and then finishes his meal.
Tosefos to Pesachim 101b s.v. כשהן and the Rosh in Chulin 6:5 both write that one need not make an immediate birkas hamazon, but may continue eating with a new hamotzi and make a birkas hamazon on everything when he is finished.
The basic answer is that not only may you, but you must return to where you ate if you can.
Practical Halacha says
After eating or drinking the required amounts, you may say bracha achrona (including birkat ha'mazon) as long as:
You are still satiated after having been hungry and eaten,
You were not satiated after eating and it is less than 72 minutes since you finished eating.
Reason We say the effects of food last for at least 72 minutes and that 72-minute period overrides becoming hungry again even after having been satiated.
However, it does not give the sources.
Halachipedia dealing with the time limit says:
How long does one have to say Birkat HaMazon?
If one ate bread and is full, preferably one should make Birkat HaMazon within 72 minutes and after the fact, one may make it as long as one is full from what one ate. However, after 72 minutes, if one is a little hungry, one can no longer make the Birkat HaMazon. 
If it’s past 72 minutes and one is in doubt whether one is still full one can make Birkat HaMazon, yet, it’s preferable to eat another Kezayit before making Birkat Hamazon. 
However, if one just had a Kezayit and was not full, one should try to make the Birkat HaMazon right away and if one didn't one may only make Birkat HaMazon up to 72 minutes after one ate. 
Some add that if one waited more than a half hour it's preferable to have another Kezayit of bread before making Birkat HaMazon. 
If one has a very long meal and continues to have appetizers or drinks, one may make the Birkat HaMazon as long as the meal continues even 4 or 5 hours. 
One should have something to eat or drink every 72 minutes, however, if one didn't then one may still say Birkat HaMazon. 
 S”A 184:5 writes that one may Birkat HaMazon until one is hungry again. Vezot HaBracha (pg 49, chapter 5) and Yalkut Yosef (Brachot pg 300) rule that if one didn’t make Birkat HaMazon until after 72 minutes, one may surely recite Birkat HaMazon as long as one is still full and one isn't hungry. Vezot HaBracha quotes Rav Elyashiv who says that it’s preferable to eat a little more before making Birkat HaMazon. Aruch HaShulchan 184:7 and 8 writes that since we don't know the precise determination of when we're still full must make Birkat HaMazon within 72 minutes and if one didn't then one should eat another Kezayit and then say Birkat HaMazon. Kaf HaChaim 184:28 writes that in order to fulfill all opinions if it has been 72 minutes one should eat another Kezayit and if one doesn't have bread one may make Birkat HaMazon as long as one is full.
 Mishna Brurah 184:15, Vezot HaBracha (pg 49, chapter 5)
Yalkut Yosef (Brachot pg 300), Mishna Brurah 184:20
Vezot HaBracha (chap 5, pg 50)
 Mishna Brurah 184:18, Vezot HaBracha (chap 5, pg 50), Yalkut Yosef (Brachot pg 301)
 Vezot HaBracha (chap 5, pg 51) quoting the Magen Avraham 184:9
dealing with having left a place and having forgotten to bench says:
If one left where one ate:
If one ate and left that place intentionally, one must return to the place where one ate and if one made Birkat HaMazon in the second place one has fulfilled one’s obligation after the fact.
If one ate and left that place unintentionally, one should return to the place where one ate unless there’s a great need. 
This is only the case if one doesn’t have bread with him in the second place, however, if one has bread in the second place, one may eat it there (eat a piece even if it’s less than a Kezayit) and then make Birkat HaMazon there. (This doesn’t mean that one may leave one’s place initially but only in a after the fact situation.) 
According to Ashkenazim, Al HaMichya should be said in the place where one ate and so if one left it would have the same law as Birkat HaMazon. 
 S”A 184:1, Mishna Brurah 184:5, 184:7
Mishna Brurah 184:12 quoting the Gra