Out of curiosity I decided to 'weigh' the table by proxy. I weighed a 27cm offcut from the legs which came in at 7kg (unoiled). Based on this the rails, which are the same depth but half as wide will be 3.5kg per 27cm. An offcut of the top came in at 5.25kg for a piece 43.5 x 17.5 cm. Calculating this out for the actual dimensions of the table gives a total weight of 290kg. I don't think it will blow away in a hurry.
Now the next job is to repair the backs of the chairs which have suffered in the weather over several years.